I felt ash was very weak

Ya your right.He lost to Trip so may times.He was not strong.

I think he also got weak.
In each of successive region,Ash's rank in the regional Pokemon increased by 2X.
It was 32 in Indigo league.
It was 16 in Johto League.
It was 8th in the Hoenn League
It was 4th in Sinnoh league.
But in BW it got back as Ash managed to get only to top 8.
Thats why I think that Ash got weaker in BW.

POINT!
I also thought that he should reach the finals this time, but I think the script writers did this to continue this series since this anime would have ended if he had won.

If the continued the trend of successing each time by the last time,the anime wont finish.
Because Ash had to still lose the Final match.Even if he wins,have all the trainers of the Pokemon world have died that they won't challenge him.Have all the other regions got destroyed.Ash still have to battle the Elite four and the Champion.Each region has its own champion.
The anime is not going to finish that way.
They are japanese people.They would stretch it to as long as they want to.

LOL YES.

Yeah.

They are still streching it. I think that Ash was meant to be weak. If Ash was strong, the series would've ended and the fans would've complained so much. Ash is not very weak. He is an awesome Pokemon Trainer. His Pokemon are great. Fans are comparing him with Red. Red and Ash are different.

You can see example of Goku.
He is strong.
Anime is finished but People still like him.