To be fair the way it worked in d2 was great. You had a closed battle.net which worked through official servers and an open battle.net where your local/twinked/hacked/whatever char could run rampant and play online with friends.
The modded versions of diablo 2 by replacing actual gamefiles is also still possible if you play it off line/local lan.
GaaS just sucks in that regard. A lot of great things came about by modding like in warcraft 3. Or even the superhero/Warcraft mods in counter strike 1.6
Or the max Payne Kung Fu and whatnot mods. I had hours of fun on that. It wasn’t the way the developers intended it to be played. But who cares.