In fact, just to give one example, we don't have JM starting a song since several albums already.. The last time he did that was on In the Presence of Enemies, or Panic Attack for a bass start with more impact..
Song beginnings are exceedingly likely to be started by one of the songwriters' instruments, mainly because it's more often than not the seed (or a variation thereof) that then became the song.
If you listen to TA, each song that isn't started by the full album is either started by guitar or keys, for that reason.
For the same reason, when MP was still around for the songwriting, you'd get an occasional song that was started by drums (6:00, HTF, TAMP). That has not happened since the switch.
You're right.. Also, another factor is JM's shyness.. But we definitely need some of that again, as well as one MM's intro.. In fact the two beginnings that you can barely say the drum is starting the song since he's in the band are BMU, BMB and Outcry, and in both cases there are actually digital drums doing those parts..
Interesting, I never looked at it like that. That makes sense; JM's one known song with him having some ideas was Lifting Shadows.
Hmm, Idk.. He's credited way more than that.. I wanna think he has contributed, in a way, at least with some percentage in about half of DT's songs.. Otherwise they wouldn't have reasons to establish the "Myung, Petrucci, Portnoy, Rudess," in the credits of a lot of songs... not mentioning the ones in which is a sure thing he participated, like Vacant, the ones in ADToE/DT12 or the songs he wrote the lyrics..