Great read from competitive reddit on how Solo Q is a better way to learn things than we think.
https://www.reddit.com/r/Competitiv...proving_while_solo_vs_improving_with_a_group/
Heres how I think of it coming from csgo. Obviously like you've said it will be hard to judge individual skill because people will stack against soloquers and have a large advantage as a result.
In that game I probably played 80% solo and 20% full party. It seems to me like you actually improve more quickly then people who stack 24/7. Your going to have to deal with scenarios where you need to hard carry more often, and be forced to rise to the occasion if you are capable. This should apply to overwatch aswell. Your individual skill will need to be on point to hard carry the bad teammates you will inevitably get. While the full stack might lack in individual skill and still win, so they wont be "forced" to improve individually as a result.
When you do eventually join a team you'll have those benefits of being a strong individual player. It probably varies from person to person but imo that individual skill is harder to develop then the communication skills you need to function within a team. At the end of the day its a shooter, strategy plays a role but if you are significantly better at clicking heads than your opponents, the impact is large.
Actually improving is all you should worry about dont concern yourself with what rank the game says you are. If you want to be as good as the best your going to have to be much better the top ranked players that queue on blizzards servers anyway.
https://www.reddit.com/r/Competitiv...proving_while_solo_vs_improving_with_a_group/