You said you had just broken a losing streak, so in addition to performance modifier you also probably had a losing streak penalty still in effect.
As for performance based SR, it compares you to the average performance to others at your rank, on that same hero. Medals compare you to your team, regardless of hero or role. I don’t think anybody knows exactly which stats are considered, but it’s likely that it considers most of the per-ten-minute metrics, damage/10, elims/10, heals/10, deaths/10, etc.
Since it’s compared only against others on the same hero, it’s a reasonably fair metric, but you can perform ‘poorly’ for reasons outside of your control while still doing everything right from a play-to-win point of view. The obvious one is if you are support and your team is stomping… there sometimes simply isn’t much damage to heal. Worse yet, if the enemy is playing timidly, as a DPS you may not have much opportunity to damage… unless you overextend into them, where you might pad your stats, but you also might throw.
For overall good SR gains, it’s probably best to not consider performance based SR in your decisions. You’ll probably only hurt your win rate and overall SR gain for the sake of padding a few points here and there, unless of course you’re playing at a rank far below your actual skill. In that case playing greedy will help you rank up to your appropriate rank much faster. If you try to play greedy and fail then you’ll only hurt yourself.