No, you're wrong again. What you're saying actually helps MY argument. In pointing out that an adc can auto during exhaust, you give the point that , while they can still crit during it, their speed is lowered so the number of crits they can get is reduced.
Using that, think of this (we'll ignore armor and IE for the sake of simplicity):
50% Crit chance for 4 attacks with 250 AD should average out to 2 crits (500 x 2 = 1000) and 2 normal attacks (500)
Totaling 1500 damage over 4 attacks.
Yasuo, on the other hand, at 50% Crit chance, actually has 100% because of his passive. So 100% crit chance for 4 attacks with 250 AD averages out to 4 crits (500 x 4 = 2000) Then we take the damage reduction from his passive into account: (500 - 50 = 450) so then 450 x 4 = 1800.
That's 200 more even without his Q. Keep in mind he's also tied for maximum melee range.
THEN we can factor in his Q, which by the time you have that much AD will have a base of 100. At that point they do more damage than his basics, while still applying all on-hit effects at a high range. We will mention that after 267 AD (with infinity edge) his basics will hit harder than his Qs.
But now let's put lifesteal on that.
Same setup.
We'll give them both 10% lifesteal, as the lowest amount you'd have with a single tier 3.
First: 500(per crit) x .1 = 50. So 50 for the two crits and 25 for the two non-crits in those four. 50+50+25+25= 150. or 450 for 30% LS.
Yasuo: 450 x .1 = 45. So 45 for the four crits. 45 x 4 =180. or 540 for 30% LS.
A 5% decrease in LS effectiveness, while it would hinder him with only 10%(cut to 5%), would at 30%(cut to 25%) make his lifesteal EXACTLY as effective as the other character. 450 x .25 = 112.5. 112.5 x 4 obviously = 450. Which looking directly up, shows you it would make his lifesteal EXACTLY as effective as the other case, while still dealing more damage with his critical strikes.
Check and mate. It wouldn't be a nerf that cripples him, it would be a balance change that does nothing to the fact his 100% crit chance does more damage while making sure he only heals as much as opponent with the same AS, LS, and AD.