Warning, extremely long post ahead.

The benefits mages have are long range, CC, and AoE. The benefits assassins have are mobility - and sometimes stealth/untargetability.

The downsides of mages are no mobility and usually most of their abilities being skillshots and thus being missable or blockable. The downsides of assassins are that they are melee and single-target, and that their burst is now delayed further (after the assassin rework).

So what’s the problem, you ask?

It’s that SAFETY >>> MOBILITY.

Mobility only means anything if you can successfully get in, kill the target, and then get back out. For multiple reasons, all of the squishy carries that would be a mage or assassin’s target must be killed instantly, because otherwise it is impossible to kill them, whether it be because of lifesteal, shielding items, healing items, peeling, or the arguably overloaded Exhaust summoner spell.

Sure, assassins are able to flit around quickly and occasionally flank.

But what happens in the critical moment where the killing must actually occur?

All assassins (with the exceptions of Kha’Zix and Rengar) must wait some large amount of time for their burst to fully take effect. Because of the above stated reasons, this is impractical to actually killing any important target. In addition, because they are melee, it is easy to CC, Exhaust, peel, or even kill them, due to them being in point-blank range and entirely single-target.

What about mages?

Mages have no mobility, so they are vulnerable to someone jumping on them, correct?

Well no, not exactly. First of all, unlike assassins, mages are always with the rest of their team. They have no reason to leave the safety of a team because they are ranged and have AoE abilities. There is no reason to jump into the dangers of close proximity to the enemy team because of that reason either.

What about burst power levels? Do assassins have stronger burst damage than mages? Nope. Both of them have enough damage to delete a carry if allowed to do so. But which one will be more consistently and safely allowed to do so? The mages.

Portions of mage abilities (and sometimes rather important ones) can be blocked by tanks. This includes abilities such as Lux Q, Ahri E, Vel’Koz Q, blah blah blah. BUT. The majority of mage abilities are ALL AoE. This means it is quite easy to circumvent the blocking potential. This includes abilities such as Brand’s W, Malzahar’s Q, Lux E, etcetera. In addition, almost every single current relevant mage either has a point-and-click ultimate or a massively large AoE. Syndra, Veigar, Malzahar, Brand and others fall under the first category. Lux, Annie, Viktor, Orianna, Ziggs and others being the second.

Now, assassins mostly have point-and-click abilities. That means it is much harder for those abilities to miss, in comparison to skillshot or delayed abilities such as the ones listed above. However, unlike the mage, the only chance an assassin has to use the ability is in point-blank range.

In lategame, both mages and assassins have fairly short cooldowns on all abilities including ultimates. Mages are free to test abilities at long range. If they do not land it, they can simply wait a few seconds and try again, or at the very least, not put themselves in a dangerous position. Assassins must use the abilities at close range. In addition, to get in said range quickly enough to not be stopped, they must either flank or use their mobility tool. If they use their mobility tool, there is no escape for them if they fail against any sort of intelligent team.

This was the problem with the Fizz rework as well. His engage potential was completely shoved into his ultimate. If he landed it on the ADC or mage, he could go in for a kill most likely. If he didn’t, he could do absolutely nothing except waiting for the next ultimate to come up.

Also, mage players at any higher ELO level will land most of their abilities. Even if they don’t, by mid and lategame, and any time in the game with teamfights specifically , landing any ability, ESPECIALLY crowd control abilities, is almost certain death for squishy victims, or at least major chunking of their health, enough to take them effectively out of the fight just as death would.

The point is that assassins get no second chances if they fail. THEY SHOULD NOT EITHER. If they fail in an engage, they deserve to die. However, the issue is that mages simply outclass assassins. If mages fail a killing attempt, they can just wait and try again, from long range. THEY SHOULD NOT DIE. Unless of course, they failed in positioning or such otherwise. But they are long range. They should have more safety. However, in terms of the killing job itself, assassins SHOULD be better at it. Otherwise, there is next to no reason to even pick them.

Low ELO and people being out of position leading to assassins becoming fed doesn’t matter. Smart players won't do that. In teamfights, mages outclass assassins in just about every single way.

This is similar to the case with Ahri. For instance, a pure burst mage such as Brand or Veigar will almost always have higher burst than her. Theoretically, let’s say 2500 damage in compared to 5000. But so what? Tanks aren’t the target. The carries are. Tanks can be just held back by CC. The carries are the ones doing the damage.

Ahri trades damage for safety. Except carries don't even have 2500 health come lategame, so the trade in damage barely matters. If Ahri lands her E, they will die. The end. The only difference is that Brand or Veigar could probably do it quicker. But Ahri can still certainly do it quickly enough to kill the carry before they can do anything to survive.

In return, what does she gain? Mobility while keeping the LONG RANGE, and in turn, even more safety.

That is why Ahri may not be overpowered by any means, but she is simply too safe of a pick and strong specifically BECAUSE she is well-rounded in every single option.

So what's the whole point of this wall of text? It's to show why Assassins will never be better than Mages unless significant changes are made, because immobility and range is so much better than mobility and melee, because the former grants safety that the latter will never have.

Sure, assassins can escape on their own if they haven't burnt their mobility ability to attempt an assassination first. But that means nothing when their sole purpose is to assassinate.

Mages generally can't escape. They don't need to though. Between Zhonya’s and multiple items with health, resistances, or other potential lifesavers (Protobelt dash, slows on items, etc), CC, range and AoE, and them always being with their team, it is unlikely they will ever be the first to die, or die at all, unless the rest of their team takes at least a few deaths as well.

This is why mages will always be better than assassins because range and immobility gives safety (not even counting CC vs lack of it) while melee and mobility only gives safety up until the mobility ability is burnt. Mages get second chances because they never get in close range, assassins won’t because they burnt their mobility tool already and are now deep in the enemy team. Mages also stick with their team, assassins flank solo or go solo. Again, more safety for the former the latter will never have.

And even more generally, not counting mages vs assassins, but all of League in general, safety and range is better than mobility and melee. The latter is only good in 1v1s which will never happen in lategame really, as teamfights are what dominate, and only bad players would be out of position to be 1v1’d if they were a carry. The former with safety and range but no mobility will just stick with their team and do everything from range. If they fail, just try again. No risk to themselves.

Tanks don't need mobility. The only ones with mobility are the ones that are fairly squishy. Tanks also generally don't need range because they engage in point-blank and soak up damage and abilities. So they are not relevant to this debate.

TL;DR - Immobility and Range are always better than Mobility and Melee