No, I didn't add critical strikes to Mug.
In order to make a mod with HW that is compatible with Memoria, you have to open HW on a vanilla copy of the game and generate "Spreadsheets" + "Raw assets" when saving as a Steam mod (then register the folder generated in Memoria.ini).
Yes, the defense/attack points are important. With late-game armors, you can see the big difference in damage compared to someone with a mid-game armor. The defense of enemies are almost always the same, 10 (12 in AF) but some of them have a higher defense (for instance, a very slight raise in magic defense makes the enemy immuned against Drain/Osmose in vanilla).
AF has been thought to be beatable without any form of grinding. Someone even proved it to be beatable at lvl 1.
The bonus you get from stat boosts is not that important, in particular because Str/Mgc/Spd/Spr don't change this "Attack - Defense" part of the damage formula. The best boosts you gain with this mechanics are a boost in Max HP/MP, ATB speed and various things from Spirit (a bit less in AF since the Spirit has much less impact on status durations and ticks).