Gaming

I don't think you actually let your friend fail and try to figure out how to not fail, and I don't think it makes the game better when you're so afraid of letting the player fail and apply what they've learned that there aren't actually any decisions to make, like those Sony examples (God of War and Horizon's latest entries, to be specific, were the ones that caught flak for this). That's where the fun comes from.

I don't recall any tutorials explaining anything beyond the cursory "you have to be in range to attack"

And that's all you need to know in order to determine that positioning matters. They also explain opportunity attacks.

The tutorial titled "Combat" simply tells you that there's an initiative roll, combatants are listed at the top of the screen, and during a turn, a character may take an action, bonus action, and move.

Which are a few of the things you said your friend was unaware of, despite the fact that several of these things are reiterated on most of the cards for your available actions during combat.

I've been playing Larian games for a long time and I don't remember a single one of BGIII, DOS2, or DOS ever explaining these concepts.

Me neither, but even in my brief time with DOS1, I don't recall needing to be told either. I just somehow found out that poison clouds can be set on fire, and very quickly.

This is not an insult to your friend, but just because he falls into the group that didn't catch on immediately, I don't think that's indicative that the game is bad at teaching you how to play it. The Nautiloid highlights exactly where you have to go and how many turns you have to do it. If you let him fail once and try again, presumably, he'd realize that what he was doing wasn't working and notice that giant UI element telling him how many turns he had to get to his objective.