PF2e relies a lot more on tactical decisions than 5e, so I'm not certain how well the mod works depending on the other systems it has to lean on - missing mechanics can wildly unbalance the maths due to the assumptions it's built on.

Assuming it is fully implemented though, flanking, feinting, or another way of applying off-guard to an enemy would increase that 65% chance to 75%. Intimidating the enemy can push it up to 80 or 85%. Maybe have an ally aid the attack and get up to 95%. Crits also change gameplay quite a bit due to the 10 over/under conditions. A 65% chance to hit contains a 15% chance to crit, 75% a 25% chance, 85% a 35% chance, so the additional misses get balanced out by the additional crits beyond 5e's static 5% chance. A single character generally doesn't have enough actions to apply everything themselves though, so you have to coordinate actions across the whole team to be effective rather than each member being an individual powerhouse.