you can disable bixby. they even have a little button inside the app where you can turn it off.moved (by force) from s5 to s8. It is filled with preinstalled, battery hungry glut for which I have no use or control (cant remove or disable)...Bixby being one. Since update to Oreo, it's slow w many glitches/crashes of it's own builtins. I might look elsewhere, even last years something for cheaper.
For the S9+, if you value much better sounding speakers, better low light pics, optical zoom (digital is fake zoom) and about 20% better overall performance, then could be worth it. Not sure though most would notice the performance increase unless you play emulators or use the Dex Pad.