I don't know what toasters you are running, but I haven't had any crashes.
Like I said, artificial difficulty. Pumping up stats instead of improving tactics or making the enemy abilities more unique and requiring the player to change his tactics.
They do different tactics too, for example in POTD they are much better at interrupting your spells and abilities, they are more likely to focus fire your squishies etc.
POTD just adds +2 armour and pen, which just makes armour buffs, armour reduction abilities, pen increasing modals and flanking much more important. There is nothing "artificial" about it, it makes you use more of your tools and indeed while in hard you can attrition grind much more easily in POTD you have to be more on top of your game to use your abilities at right times.