Having a spread with one -2 is much worse than two -1s IMO, because a -1 basically says you don't want to play the matchup, but if you outplay your opponent there shouldn't be anything to prevent you from winning, there is not a single character in bracket you have to fear. However having a -2 means that there is a character who even if you outplay your opponent, you can very likely lose to, assuming solo maining, that is exponentially higher odds of a bad matchup even if there are less bad MUs. That's why Mario and Rosa in particular are lower than M2/ Sonic, even if I feel their total spread is better and their tournament results are better, they have a higher chance of just running into a matchup that their mains should consider a secondary for.
Edit: However, if you have 4 or so -1s, that's probably worse than a -2 just because that means you consistently have to play at disadvantages, and in tournaments mental stamina is absolutely a factor, no one is a robot, no one is perfectly consistent, the more poor MUs you run into the higher likelihood of losing that MU, and at some point it's more likely to lose one of your four -1 matchups in a row than it is to lose your three 0 or even +1 matchups and your one -2 matchup.