About the aliens on Voyager, the journey home was suppose to take 70 years. In the beginning they spent a lot of time jumping around solving problems and fighting the Kazon. It was far from a straight line. They even had to back track on occasion. (Cathexis, Faces, Jetrel, Manoveurs, The Basics just to name a few). Makes sense they did not clear their space quickly. The first major leap forward happened in The Gift. No more Vidian or Kazon.
The Hirogen were nomadic so finding them scattered around the delta quadrant wasn't that big a stretch. Same with the Borg but they are a Next Gen original so don't count.
You have me on the Talaxions. Geesh... how stupid was that, but this was close to Endgame and I simply don't want to even think about that episode. If I try really hard I might be able to suffer from a limited form of amnesia and convince myself it never happened.
Ok it didn't work but I tried.
My point is if other series can do it, why can't Discovery. Big universe...lots of potential and it doesn't have to mess with canon. They simply disappear before the series finale. Sort of like the spore drive.