They have multi-cart solutions for the MSX/2 but the thing that gets me about it is that it doesn't even support screen scrolling.
You’re correct that the original MSX doesn’t support screen scrolling, but the MSX2 does. And a lot of the best Konami scrolling games have now been patched by the community to support the scrolling hardware. Do some YouTube searches on Salamander Enhanced and Nemesis 3 Enhanced for examples. And using a flash cart like the MegaFlashRom makes it easy to run the patched upgrades and translated games as well.
OP, I recommend the MSX over the C64 if you’re interested in some Japanese developed gems from companies like Konami and Compile. The MSX got unique entires in the Metal Gear, Snatcher, Golvelius, and Aleste series. The home brew scene is strong too with some good recent releases from Kai Magazine Software, among others. There’s fun expansion options like stronger audio processors and the ability to run Sega Master System ROMs as well. Just be sure to go for a late-model rig like a MSX2+.
The Commodore 64 has some good games as well, but mostly from US and European developers. I personally feel the Japanese were ahead in game quality on 8 bit games from the 80s, but that’s just IMHO.