hm....I have yet to watch it, but in the end, I feel like the match between trip and ash was okay.
First of all, I have to say that pikachu, being the speed small pokemon it is, would end up dodging frenzy plant if he did keep it, and since Serperior's tail would be stuck in the ground during the launching of the move, He'd be a sitting duck, perfect for ash to hit down like he did right in this battle.
As for solarbeam...I think that the reason why it fired so fast in the world tournament was because the sunlight was strong. You saw that everytime he used it, they aniamated the sun to show it gleaming. Therefore I think trip took advantage of that. They could just say that wasn't the case here.
Solarbeams questionable, but frenzy plant defiantly wouldn't have hit pikachu if they wanted it to win. Its perfectly plausible too, even by game standards. In game it has 90 acuraccy...lol
May I ask what the "wave motion" thing that riolu did to emboar? That was really cool. lol