>>57961374 (OP)I'm a big fan of pre-3DS Pokemon music, especially Gens 1-3, and this is something I've always been curious about and I'm surprised to find a thread about it here.
My only guess is that they wanted RS battle themes to have a "bold" sound while simultaneously being a bit minimalistic (GF limited themselves when it came to GBA sound channels), and Masuda just happened to land on timpanis while screwing around. Also, in a general midi soundset, if you pick the "orchestral" setting for the drum channel, timpanis are in place instead of toms, which many other soundfonts and VST plugins follow, so that probably inspired it as well.
It saddens me that with all the leaks, we didn't really get much if anything at all on the music development for RS in particular.