At level 10, you can get Dex 20 and Con 18. If you play variant human and use your free feat on Unarmored Defense, that gets you AC 19. A fighter without the feat at that level would have AC 17.At roughly level 10, a dex fighter would have 20 AC and about 114 HP without a fighting style which is ahead of the curve defensively.
You can add a shield if you like, but the fighter without the feat can add a shield too. It doesn't change anything--you're still only getting 2 points of AC from the feat. And that's for a fighter. Non-fighters have to wait till level 12 to get even +2 AC.
Wait a minute, you're excluding variant humans? And you are proposing to have 20 Con, 20 Dex, and a feat by level 8? That's five ASIs. Fighter gets you three. Where are you getting the other two?It isn't hard to get 20 con by level 8 as a fighter, and I'm excluding variant humans which can afford a feat for free.