You can get away with low Dex if you have heavy armour proficiency, neither bonus nor penalty apply to AC.
Likewise, having enough HPs, resistance and many magic bonuses help offset an average-to-low Dex.
Yes, falling prone is a worry. In BG3 that immediately ends your turn - but there are items for that.
No, the biggest concern I think is the low initiative. I suppose you can build tactics around this to lessen impact on round 1 when it matters most. There is also the Alert feat which instant solves the problem.
There's also those gloves of Dex in Act2? I had my paladin wear them and it was great. Decent missile attacks, lock picking and initiative.
