DA:O and DA:I are in the same league for customizability. If you think those (or really any modern 'RPG' other than a few that came out last year like Divinity: OS) are in the same league as BG1/2/ID1/2, you obviously didn't play those games.
Its laughable to compare the two. And yes, I like both genres, but they are leagues apart.
I've played every game you mentioned.
DA:O gives each character roughly 80 talents to choose 25 skills. You can mix and match them in a lot of ways. Not to mention 40ish skills, and stats. I felt like I had a lot of different ways I could mix and match my characters.
Divinity: OS has fewer skill choices, though a skill point gives you access to a lot of spells/abilities. To be honest, DA:O felt a lot more personalized on each character than Divinity: OS, because as you max out your skills, you then could buy every spell/ability in that category. I felt the higher level I got, the more generic each character was.
You obviously have a very different view of what we could create in those games.
It really, at least for me, came down to how you could give each character personalized abilities. In DA:O, I could create a tank rogue, I could create a Backstabbing rogue, or a stunning rogue. I could make a support rogue and so on. As I got high level, they maintained their personality, and even became more specialized in a way.
In Divinity: OS, I found my characters had a lot less personality. As a warrior, I was a tank, or DPS, but ended up with the same skills. If I played a rogue, I would either be an archer or backstabber, and I just had one set of skills or the other and end up with both by the end. The mage had the most choices, but in the end, they almost always end up with almost every spell, and one or 2 trees that were slightly less filled.
I just didn't get the same experience you seem to have.
Edit:
And if you want to compare to AD&D based games of the past. That was my point. They were overly complicated on builds, yet when you played them, melee was almost entirely passive, and mages had fewer abilities, even then. It isn't that you couldn't add a larger list of abilities to choose from either.
My issue with AD&D for modern RPG's, is the character building was overly complicated. If you wanted to pick a spec, you better have picked many very specific abilities as you leveled up. That sort of thing is not needed and melee in AD&D is a snooze fest compared to modern games.