Don't you just hate how the bike just doesn't want to stop and it feels like you're falling behind constantly? Here's a couple tips to make these three trophies dumb easy with a bit of practice from a racing game newbie and little to no practice for someone who plays racing games a lot.
1. Forget Career, do this in World Championship: Bikes are in what we call BOP, Balance of Power so bikes have very similar power output. Just pick a top row rider to swat one opponent out of your way.
2. Turn off Traction Control and Front Brake ABS: I know this might be scary but the bikes are not that uncontrollable while these are off, you just have to apply some throttle control when exiting corners. Front Brake is the one bound to L2, you will still need to use the Rear Brake that's bound to Square but you will brake so much faster than ABS on.
3. From long straights to the next corner, brake early!: Don't trust the racing line on this game. The physics of the bike and the useless brakes make it kind of useless when braking. If you miss the corner, apex or go off-track at anypoint, remember to abuse the Second Chance option.