Anything running ignite can 100-0 a marksman
Ignite is clearly balanced against the heal/shield-excessive ardent censer meta - the one that stopped existing over a year ago. Today, ANYTHING with ignite can easily 100-0 every marksman in the game that hasn't completed their 5th item yet just by using all the spells in their kit once. It doesn't matter what you're playing - flash ignite RQWE and the marksman WILL die.
Before you call me out as an adc main, i'm a top lane main. I main juggernauts. My favourite champions are Mordekaiser and Darius. I don't even play marksmen (i used to play bruiser Ezreal top before they made sterak's gage melee only and i might have played a game or two of tank miss fortune/kog'maw in seasons past, but that's it for my ADC experience.)
Marksmen are getting blown up in less than a second by EVERYTHING. Tanks? Check. Supports? Check. Mages? Check.
ANY mage with one completed item can drop a marksman (even one with 3 completed items) in less than 1.5 seconds. Sure, unlike old Talon and DFG Leblanc the marksman actually gets time to blink - but what does that change? They can see what kills them. They still can't do anything about it, because for every 50 damage they deal to their aggressor they take 500.
You know what doesn't blow up marksmen, though?
Other marksmen. That's the only class in the entire game that can't reliably 100-0 a marksman just by flattening the QWER keys on their keyboard.
How many champions are we at now? 140? And nearly EVERY SINGLE ONE OF THOSE can 100-0 a marksman just by smashing their face into their keyboard and dropping ignite on their victim.
Everybody knows by now that damage is excessive. It needs to be toned down across the boards - so why not start with the most universal offender, the one that allows players to succeed without even having the slightest clue how to play their champion? Ignite isn't limited to what champion you pick. And if nerfing ignite indirectly nerfs other champions because THEY DEPEND ON THAT SPELL SO MUCH THEY ARE FORCED TO PICK IT EVERY GAME, then perhaps that'll help pinpoint what else needs work?
and 
, shields are not a viability any longer.
's used to last for 4 seconds, now it lasts for 2.5 seconds.
's used to last for 6 seconds, now it lasts for 2.5 seconds (I know Pix still lasts for 6 seconds but we're talking about the shield itself here).
's shield even decays over time.
got it's passive reduced by 3%.
and 
got their passives reduced by 2%.
got it's passive reduced by 5%.