Poe's super durable and can often survive to the endgame (if your opponent doesn't focus him down early), but he has some innate weaknesses. Firstly, he's an ATT3 gun that costs 40+ points. He's not going to do much of anything to your opponent's list, just like they won't do much to him. He is, in essence a "bank" for your squad points.
He gets pretty hard countered by anything with 4 attack dice, in particular Lone Wolf Dash, as he doesn't have the maneuverability to match.
Thweek (with an appropriate initiative bid) is pretty much his worst matchup, since he can stay behind Poe or outside his arc while getting TL modded shots indefinitely until he dies.