To be fair, between backgrounds and archetypes, you can achieve much of the same build customization that you do with more classes and multiclassing in 2E.
Nah, this is a combatfag game. Backgrounds, languages, skills barely matter, especially as you can be proficient in everything with your party through minimal planning.
The only things that do matter for gameplay are class > attributes > race in order of importance. Both 2E and 5E attribute system have about the same impact, for 5e put mainstat and con to +3 and rest to whatever, for 2E put mainstat, dex and con as high as you can and rest whatever.
Icewind Dale has significantly more classes, and higher gameplay diversity among the classes. Solasta does not even have a druid, let alone something like a shaman.
Claiming Solasta has more customisation than IWD borders on trolling.