I assure you a Yasuo that builds full glass cannon is going to die in the snap of a pair of fingers. Now lets look at his base stats:
Health: At Level 1 he has 517.76, has the growth coefficient of +82 per level, and has 1911.8 at level 18. Shen is the tank/tanky champion with the lowest base health at level 1 with 540. Don't get me started on the champions with more health than Yasuo at level 18. Vlad, Ekko, Zed just to name a few damage-centric champions with higher base health. Not to mention all the tanks.
Armor: At level 1 24.712, with a growth of +3.4 per level and a max of 82.5 at level 18. Now, here Ill give a bit of credit to you; at level 1 he has more armor than some tanks and juggernauts, Amumu, Sion, and Alistar to name the ones I payed more attention to. At level 18, however, he only has more base armor than Sion (because of his health stacking ability; forgot which one), Shen (because of his passive), Trundle (because of his passive and his ultimate), and Sejuani (because... I don't know, too lazy to check on her abilities). Otherwise, all the other tanks, and some others have higher base stats.
Magic resist: 30 at level 1 and 30 at level 18. Nothing to say here.
In reality, Yasuo is tankier than most mages, some tanky-champions and some ADCs. Why? Because he's in the middle of the fucking battle and he doesn't have the range advantage that these have. He's in the position of highest danger from being blown up. And the tanky champions that fall behind him in base stats all have some form of artificial tankiness that make up for it.
Now, a Yasuo that knows what he's doing and isn't a Diamond smurf screwing around in Bronze, he's always going to build some items that beefs him up. Even in mid lane, where the lane is obviously more damage-centric, he's going to build at least one, usually two defense items, whether it be damage-defense hybrids like Frozen Mallet and Gage, or full-out defense like Guardian Angel and Randuin's Omen, or one and one from anything that falls in both groups.