If the game won’t allow you by matching you against full teams while playing solo?
Don’t go solo. I personally love going solo I tend to do better. If you want to rank up find quality teams. That’s why achieving a high rank in Halo 2 days meant something. Because if you kept losing you would derank. So obviously the better players and teams have the highest ranks. Gave you something to strive for. Got to get better or play unranked.
I believe the game tries to match solo players against solo players first. So if your search time is too long, then back out and restart the search to get the best results.
Best place for feedback on this is the Matchmaking feedback thread in the MM forums. I would also check out the archive threads amd previous weekly topics for an idea of the changes hat have been made to make matchmaking better.