> No notable audio production software or soft synth plugins is Japanese, which is weird, considering that many of their synths are digital in nature
Have you tried KORG Gadget? It's incredible and a solid DAW/virtual studio in its own right. Basically a killer app for the iPad, and it's also available for macOS.
All of KORG's music apps are fantastic, and basically reason enough to buy an iPad: Gadget, Module, ODYSSEi, iWavestation, iPolySix, iMS-20, iMono/Poly, iElectribe (and its Wave and Gorillaz variants), iKaossilator and iM1.
In addition to PC/Mac/iOS, KORG also has even ported several of its music apps to the Nintendo Switch and 3DS/DS. Definitely fun to make music on a gaming handheld.
KORG is one of my favorite music software/virtual instrument/plugin developers, hands down. And they've been on fire in terms of hardware synths over the past few years as well, both with new/affordable analog as well as classic reissues.