I don't really understand your first point. You have written a bunch of mage items that give def-stats. I don't really see the point of it. Mages kinda need those HP items to deal with their opponents. Or maybe you think squish mage vs assassin is easy :P?
Then this:
and please don't pull the,well adcs can build X/YZ
Not only they can and it is somewhat viable option for some of them, but they also have a support just for themselves for 90% of the game. A whole 1 champion dedicated to make ADC buy less survivability. But that is beyond the original point, so lets skip it.
Buying just one item,for example ROA,will give you 500 more HP than the adc,get Morello and now youre 800 HP up on them
First: For what it gives ROA takes a solid 15 minutes to stack. That is 15 minutes of you focusing on better survivability rather than damage.
Second: Do you know whay mages have so many HP-stat options in their items? Because in this powercreeped DMG meta, everyone would kill them before they'd even cast a spell. Sure, a mage with bonus 800HP more than ADC looks intimidating untill you remember that he's useless without his abilities and even those are below average, as he focused on HP items instead of AP.
Do you know why ADCs don't have to buy defensive stats as first, second or even 3rd item? Ofc beyond the whole case of them having a support behind them? Because they have better options. ADC that missed his power spike is useless. A Mage that missed his power spike is just a support.
Mages have more inbuilt survivability compared to most ADCs.
Because they are either close range, or their cooldowns make them useless for 10-15 seconds between bursts. So they NEED HP to survive for the next shot to be fired. Also they need whatever survivability they need in lategame when ADCs could crit-lock them for 300/hit. Something their basic spells cannot do.
There's a reason ADCs aren't played MID vs Assassins but mages are
Yea, waveclear and ganking. Also the fact that ADCs without supports nearby tend to die pretty quickly to assassins (as it's supposed to be).
And no. Mages aren't played mid for their shitty sustain or shields. It's because they have NOWHERE else to go. sustain/shields are the solution for them to be viable in mid lane.
Listen, when we used to have WOTA with its spellvamp, it hardly made a noticeable change. Unlike ADCs, mages (at least 99% of them) cannot crit with their abilities. The spellvamp was even further reduced to DOT/AOE damage. By no means was it game changing stat. If anything buying WOTA would actually serve as buying less pots.
Spellvamp as a stat was heavily unhealthy only on 4-5 champions out of all. And by that time every SV enthusiast asked Riot to rework it, if anything, rather than remove it completely. There were few decent suggestions for SV to be reworked into healthy stat. But it was taken away like that. And you know what else? The 4 champs that 'abused' it... were soon after reworked............................... Yea. Fucking great.
Lastly, you should know that lifesteal (and spellvamp) as a stat are actually hurting this game by alot. Their existence (well, not SV anymore) reduces the possible power of supports, which in fact makes playing supports feel like a tedious, boring, annoying work.
Here's an example: Do you know that in HOTS lifesteal is quite rare and pretty weak stat? You know what does it do for the game? There are supports in the mode, that have BASIC ABILITY heals that heal you for 50%+ of squish health, a cast. In HOTS playing a support FEELS powerfull. It FEELS FUN. In LOL, however, I'd need a solid 3 minutes to fill HP of some ADC squish with raka in early game. And In lategame my heals become useless. Either they hardly fix a scratch, or ACs have BTs and outheal every damage with 1-2 autos.
But that's the other thing.
My very first point in this thread was: Riot removed weak-ass spellvamp from the game, while calling it unhealthy. Yet they see no issue ADCs running with 30% lifesteal, a game critting people for 300+ and pretty much outhealing ANY damage they get. Some mages would absue it? Then how about rework SV that wouldn't be abusable, hmm?