I wouldn't say much lower. My reasoning is just take a look at the league leaders in any European league. Take Italy for example. The vast majority of the leaders in scoring, rebounding, assists, etc. are NCAA nobodies. No offense to them, but it's true. The only areas where the Europeans dominate is in FT% and 3pt %, which fits in with my belief that Europeans are great at unguarded shots.
I played in the second division in Torrelavega at Juventud Florman. I am aware of the difference in quality you point out. Sabonis (greatest big man ever) played in the ACB shortly after I left Spain.
Once I scored a basket that still makes me laugh.