Wouldn't the negative DEX knock 1 off your AC?
Isn't dodging a fireball down to a DEX save?
Not sure with 5e/Larian but it used to be the case that fighters need a 13(?) DEX for a certain feat (or skill). Or am I remembering that wrong?
1 - I'm fairly certain that AC is not affected;
2 - Fireballs, Burning Hands, etc. - that's what I'm potentially worried about

But my CON 16/18 should handle that :P;
3 - in PnP Fighters need STR 13 to don heavy amour (Larian no use). A DEX 13 requeriment might had applied to Rangers?