It's not 90K soldiers in Europe, it's more like 55K and getting smaller all the time. The "goal" is 28K.
Right now we have the equivalent of a reinforced Divison (two Maneuver Brigades, One Airborne Brigade, One Artillery Brigade and one each MI, MP, Engineer and Aviation Brigades)
They are based mostly at Major Training Areas (Grafenwoehr and Baumholder) with Landstuhl/Ramstein/K-Town and Weisbaden being the next largest places.
We are down from over 800 installations in 112 Communities to now being just over 100 in 8 communities, having just recently closed up everything in Mannheim, Heidelberg, and Wuerzburg.
At the height of the Cold War we had 4 Full Heavy Divisions (1st Armored, 3rd Armored, 3rd Infantry and 8th Infantry) of 3 maneuver brigades each plus an Artillery and Aviation Brigade each. There were also 2 Forward Brigades of one each from the 2nd Armored and 1st Infantry. 2 Armored Cavalry Regiments (2nd and 11th) which were "pocket divisions", and 2 each Artillery, Aviation, Engineer, MI, MP, and Signal Brigades along with an Air Defense Command (a Brigade plus of duck hunters). Roughly 215K soldiers total.
Europe does give us a forward base from which to have forces forward deployed and support operations, along with some places to train. Since we are no longer defending them from the Russian hordes, USAREUR does serve to let everyone over there know not to screw with Uncle, nor try any of the crap that started War I and hopefully settled it to everyone's (well, at least our) satisfaction in War II.