Your timing for grabs is horrible.
Let's be a bit optimistic, eh?
A good effort! Not a bad fight against the Italian Stallion!
I'll cut straight to the chase. Yes, what Jarri said was true: Your timing for grabs..could be better.
There are a lot of things which needs to be improved on, but I believe your main weakness was your...predictability.
You need to play the game with more variety. Use more moves, instead of just D-Smashing and F-Smashing.
You won this game, but if you're up against a smart and cunning opponent, you're in big trouble.
You also need to think about how many projectiles your opponent has.
Mario only has a fireball projectile which is affected by gravity. Olimar has one of the most damaging projectiles in the game, and can throw up to six. You gotta throw more Pikmin, buddy! What can he do? He can't just stand there and let Pikmin chip away at him! He has no option but to come at you!
Now you meet him head-on and grab him. D-Throw and F-Air, not D-Throw and Up-B.
D-Throw+F-Air will do more damage than D-Throw+Up-B.