I think teams often struggle for the rest of the game when the starting QB goes out regardless of who the backup is. Teddy went 5-0 as a starter in 2019 but when he had to come in for Drew middgame in week 2 vs. LAR he looked bad and the team looked deflated. I don't think it's entirely a "the team just doesn't believe in Jameis and knows he's the worst and boy they all would've just magically played better if Taysom played." (not saying that's exactly what YOU said but that seems to be the sentiment among some).
I also disagree that "we could all feel that it was playing out different than last year." Winning close games involves a degree of luck. We got lucky Tannehill missed two wide open receivers vs. TEN. If you play a ton of close games, your luck is going to even out eventually even if you go on a run like MIN did last season (if you include their playoff loss they have now lost 4 close games in a row after winning 12 in a row). We've played 3 one-score games and are 2-1 in them. That's a fairly normal degree of luck. And last but not least, I disagree with your statement b/c our OL was so obviously terrible and when you have a terrible OL, you're just biding time until your QB finally gets hurt.