Don’t really know how to define them, apparently Steam classifies GD and TQ as Isometric as well, but they feel more of ARPG/Hack&Slash RPG to me. By the title I’m referring to games like:
- Baldur’s Gate
- Icewind Dale
- Neverwinter Nights
I personally consider myself as an RPG addict. From ARPG/H&S, Western (recent bioware/bethesda releases) to J-RPGs. I’ve played most of the mainstream titles and have done reasonably well. However, I can’t say the same for the Pen & Paper ones, and truthfully, I really think it’s not for the lack of interest and research. It’s just that I find myself horrible or below your average player in terms of grasping their concepts. Would love to be able to play these kinds of titles at their highest difficulty someday. As an RPG player, everyone who considers him/herself one should experience the "roots’ of RPG.
Thoughts and advice?
‘‘Isometric’’ refers to the camera view. In that sense, Grim Dawn and Pillars of Eternity and Wolcen and Divinity: Original Sin are all isometric games.
ARPG/hack’n’slash refers to the sub-genre, just as CRPG, or pen and paper RPG as you call them also refers to the subgenre.
I wouldn’t sweat it if I were you. You would be amazed at just how much I suck at Grim Dawn. My first character has had 121 deaths so far. It’s all trial and error. The games you listed (Baldur’s Gate, Icewind Dale…I’d add Pillars of Eternity and Tyranny to that list), are relatively difficult, with rather complex rules and stats. It’s not surprising that you find them hard. I think a small number of players actually play them on the hardest difficulty.
The math behind these games is the same as in the P&P-RPG.
I think, BG and IWD use modified AD&D-RuleSets and Neverwinter Nights the 3.0/3.5 Ruleset. If you get an understanding with them, these games are a lot easier.
But: These games are not about difficulty, they are about story. Perhaps Pillars of Eternity/Tyranny a little bit less (they should challenge the players), but the original are more story-orientated.
Planescape Torment does this to the extreme; there is really less fighting than a lot of other games.
Play them on a moderate difficulty and have fun. I played them all. 
Well, I’ll give it a roll. I do a warm-up run on the easiest one (IWD) then I’ll progress to BG > Tyranny > PoE (I heard this game is very sadistic; comparable to xcom, but a different genre )
IWD isn´t the easiest, but it is really nice. 
Don´t forget IWD 2.