If you said to me that MM in the old QM was a disaster before they updated the roles so at least both teams would be matched for tank/healer, I’d take that onboard.
If you said the old method of using MMR seeded from QM, where players deliberately created new accounts and artificially inflated their MMR, so they could rank into Diamond (I think even Master Rank), then you would have a point.
As others have pointed out, even with these issues people climbed ranks, I started as Silver 5 and climbed into Plat, others were in Bronze and reached Master rank.
I’m not someone who will say to you “Fan can climb from B5, so of course you can too.”, because the majority of us don’t have Fan’s skills.
The counter to your argument is many players, who aren’t celebrity streamers, have shared their experiences solo climbing on the forums. A good place to look is RCW’s Hots Replay Thread.
I remember following Sami’s journey from Silver 1, to Master, or high Diamond, where they mostly played the majority of those matches solo and a great deal of those games were played with Lucio, a hero few people list as an impactful hero to make climbing ranks easier.
RCW’s thread is also a great place to post your replays to receive feedback, most people on these forums are generous and will give you feedback on your performance, without being negative or rude.
I get it and know how bad Bronze is. However, we are in 2023 now, Hots is in stasis, the player base is declining, so naturally the MM will suffer. As much as I think SL is badly designed allowing players to group as any size, and two ranks apart, players are still able to climb. I have a friend who has only been playing for about 12 months, and they climbed from B3 to Gold5 solo. Melke (Battleooze) recently climbed from Silver into Gold, I’m sure he would give you some tips.
My advice to you is just not to worry about your rank at all, very few people even care about what rank you are in Hots, especially now. Try to simply enjoy your matches, or if ranked gets too annoying (It did for me) just quit it and play QM, ARAM, or even vs AI.
Best of luck.