In crash bash each level is a different minigame (7 types of minigames, 4 styles of each, making it 28 levels) plus 4 bosses (all of them are, for the most part, autoscrollers, and specially the last boss is quite long).

For each minigame there are 5 rewards: trophy (win 3 rounds vs AI before AI wins 3), gem (win in time/score high enough faster than the enemy), crystals (special challenges) and relics (win 2/3 consecutive rounds against fixed opponents with better AI; gold is 2 rounds, platinum is 3). If we count gem + crystal as 1 round each (on average it may be slightly faster than that, but it's close enough), that means you have to win each minigame a minimum of 3+1+1+2+3 = 10 rounds. If you add the huge amounts of rng, how punishing some mistakes are and the fact that if you lose the 2nd/3rd round in a relic attempt you have to start over, it's probably about 11-12 rounds on average per level, let's say 11 on a good run.

Then you have to take into account that 2 of the types of minigames have rounds of 1:30 you can't speed up in any way (it's a score competition after time ends). The balls minigames also take about 1-2 minutes to complete just because of the rate at which balls appear (which you use to lower the opponent's score). The racing minigame takes 50s-1 minutes to complete as well (5-6s/lap, 10 laps). The other 3 modes, which involve fights and end once the opponents are eliminated are actually quite a lot faster, even in the harder levels.

So let's say it's 1.5 minutes per round on average including load times (they're sloooow... glacial) because you beat every fighting level round in under 30s, 11 rounds per level on average, 28 levels... that's around 8h right there. Add the boss fights and more realistic times/number of attempts (a great run is probably less than 8h, but a marathon run probably won't come close) and that explains the 9h run.

About the 201%: this game has 2 competing teams, aku aku's side (the "good guys": crash and coco, and uka uka lends you tiny and dingodile to make it fair), and uka uka's side (the "bad guys": cortex, brio, kong and rilla roo). When you beat the final boss, your team wins, and the ending that corresponds to that team plays. If you're playing coop and your characters are on opposite teams, there is no "neutral" ending, so which ending plays is decided in a fight between the players. And for some reason, completing that fight gives you 1% extra completion.

This forces you to pick one fighter from each team. Luckily, Tiny and Kong are just overpowered in every minigame type in which the differences between characters are noticeable, so even if there wasn't an extra 1% behind that fight Tiny + Kong would probably still save time even with that extra unskippable fight. Maybe Kong + Cortex/Brio would be viable (those 2 are the only other decent characters, really).