Morgana was the definition of a complex champion
I mained Morgana and the only thing you can consider "complex" about her is your Q predictions. Her gameplay is not complex one bit because nothing in her kit allows her to be a skill expressive champion, given how immobile she really is. And the only skill she has that does something on range is Q. Her W is basically either a farming tool or something you can couple with your Q.
Zephyr made non dashers viable.
Zephyr was such a niche purchase that the only use its ever had, was when you were selling your boots in the super late game and replacing them with it. That's it. Zephyr was never an item you'd consider unless there was literally nothing else to buy due to full item builds. And games were never dragging out that long in majority of cases.
Mages with long range weren't as toxic and had less mana replenishment, which result in pauses that lasted the entire game where you could kill them. Now.... 
can miss 70% of his kit and still do enough damage to eradicate a team and prevent them from reaching him, and have 60% of his mana left.
Nope.
Xerath did that before and his passive (proccing it on champs), allows him to replenish his mana on the double double instead on a minion. If he is never in range of an AA, spamming his spells is not ideal because all of them have a high cost, given he has a lot of range and scaling damage on them. Missing your stun makes you a sitting duck because then the skills you have are not sure hit and the enemy can fuck you up (your ult isn't something you can fire in a 1v1 skirmish).
And let me remind you that in S4, Xerath had a "stun" that marked your champion and that any of his spell procs would trigger it into an unavoidable 100-0 combo. So the mere threat of a stun would zone you out of any interaction with him. His mini rework changed his "stun to none" combo to be far more manageable and he is now rewarded with a longer stun if he can snipe you from his range, not his melee danger zone. His W now is that he had on his ult while his W before was a root that increased his range and spell pen.
I used Xerath to obliterate team Twisted Treeline games since he was so fucking broken that dealing with him was never an option unless you had a rush team and could bypass his initial stun threat.
Drakes didn't make of break the game.
They don't do that now either.
Drakes in earlier seasons actually awarded 300 gold to the entire team, which made contesting them a fucking chore if one team could always just sit on the objective and farm it reliably while the other team had to sit and watch. Teams usually didn't fight in lanes unless it's drake spawning, which meant 2-3 free drakes and you could avoid unnecessary lane fighting. And oh boy, every drake spawn was met with a bot lane fight usually breaking out because that was the objective that was the most important for getting an easy lead.
Top lane Bruisers weren't building lethality. They were building Armor, and very rarely.... crit..... which made them far more predictable and manageable. You didn't have to worry about Garen shredding you down to almost no Armor at all.
Tip lane bruisers aren't building Lethality now either...
Do you realize that if you get pure damage as a melee bruiser, you will get blown up super fast? Bruisers now (and juggernauts) build TriForce, Sterak's and BC as their primary items. Unless your name is Jayce. He can make it with a Youumu's and potentially Edge of Night.
Bounties weren't turning 1 major killer into a 1 man winner; they were rewarding the whole team if they contributed.
Uh, no.
I remember the days when the fucker who got fed was solokilling everyone and chasing kills and winning games single handedly. This is impossible with today's team standards and even now, Riot made bounty changes was back to be funneled more into the killer and less into the assisting teammates. And for the pre-season, they're changing gold bounties again that it reflects your farm as well meaning that ,for example, proxy Singeds with 0/15 and 300 farm aren't worth 15 gold and destroy you as if they're 15/0 (which they are in gold but not KDA).
You didn't have to deal with team invincibility
Tank meta was a thing back then.
That was team invincibility for ya. And no, people didn't have many ways to deal with tanks, especially not mages. And Marksmen were basically forced into BorK, where most of them weren't even synergizing with the item (except for Vayne).
We didn't have a lot of wall travelers
Every champion with a dash, jump or blink could "wall travel".
This wasn't Riot's invention after Season 4. This was always in the game. Today we have champions that have a dash but cannot jump walls (Galio, Urgot, Ornn) and Riot didn't stop giving these abilities to some new champs either. And Plants. They've maybe contributed to the mobility in the jungle but in my opinion, this is way better since even a Dashless champ can counterjungle your ass if they plan out their escape route. Before, only champions that could reliably get out via a dash would even attempt such a feat. Everyone else risked getting their ass collapsed upon, even if the enemy team responded late.
From the start of Season 4, there's only 12 new additions with unconditional mobility on basic abilities that can traverse walls. And before that, there were 34 wall jumping champs (with unconditional mobility). Even more if you count champs like Noc, Kat, Rengar, Jax, etc...
