Well, if you are gonna go solo and side projects of the guys from LZ, then you could do the same for DT (LTE, TA when Portnoy was in the band, solo albums by Rudess, JLB, Petrucci, etc.), and then they'd be just as prolific.
Plus, when talking about older artists, it is worth mentioning that albums were much shorter back then. I mean, the Beatles had a ton of albums in a short time span, but most of them were less than 40 minutes, IIRC. Help!, for example, is 14 songs and 35 minutes. Please Please Me is 14 songs and 33 minutes. I am not arguing "more is better," merely than when discussing sheer quantity, you have to take minutes of music into account, instead of looking at just the number of albums.