Funny, but PnP, D&D has been accurately and faithfully adapted to PC games for over 30 years now. Larian isn't breaking new ground here, except for making the least faithful adaption of a PC game with the D&D licence ever made. Others have managed to reproduce D&D rules and the PnP experience to PC since the late 80's, there's no excuses why it can't be done now.
Not 5e.
Seriously, the problem is, as stated, how shallow 5e is.
In AD&D, 2nd Ed, and 4e the system is designed such that focus firing on the caster might get you a downed caster, but now you're sucking whatever the melee character is bringing. 4e was specifically designed to let the DM go all in and not instantly TPK the party.
5e still weakened the fighter (compared to OD&D/AD&D), and didn't include any of 4e's defender rules, so yeah. Straight 5e means "I hope you casters didn't want to do anything other than hide behind corners" because blocking LOS is the only thing that prevents you from being ganked.
