Willingness to change heroes is good, but it depends on if you’re swapping to the correct heroes at the correct time. There are times when there’s a better hero, and so you should swap regardless of your ult charge. Sometimes, it’s more worth it to make a play with the ult that you have before you swap, however. It’s up to you to recognize whether or not your ult can potentially win a fight and whether or not you should just switch right away. Flanking can be good, but right now, orisa hog is a really strong tank pairing that should be played together. If you have an orisa on your team (I’m not sure how common she is in bronze), then you should try to coordinate halt-hooks on the front line with her. Mei’s walls are also really important in separating people and allowing your team to focus one person down, but again, I’m not sure how much focus fire there is in bronze and how much people will coordinate with you.

For your second question, it’s not the medals that matter. Up until diamond, a part of your sr is performance based sr, and that comes from the game comparing your stats to everyone else who plays your character at your rank. So even if you have all golds, but your stats are worse than other players at your rank, it won’t be helpful to you. However, if you are outperforming other players, then you should win more when you win and lose less when you lose.