No I doubt the writers would do that but look at some of the examples already, I mean look at how powerful Ash's Charizard, could you say that Charmander/Charmeleon would've been able to pull all that off?
In the anime they have said when a Pokemon evolves it does in fact get stronger (Brock said it when Turtwig evolved, even Dawn asked Ash the question, the only affected thing was Grotle's speed).
Look at in this example.
Suppose Pokemon Grass Type A has Razor leaf but because it's not that strong as it possibly can, its razor leaf can't cut through a cage. But then it evolves and it can break the cage, because after all it did increase in strength.
I think you are taking two different species of Pokemon one is the pre-evolved of the other and comparing them to each other.
You can't do that, you have to take the Pokemon itself and think of what happens when it evolves.
Ash's Floatzel would be in fact stronger than Ash's Buizel. But that doesn't mean Ash's Buizel is weaker than some other trainer's Floatzel. After all those are two entire different Pokemon, it would be obvious why Buizel could be stronger than it. But to say if Buizel evolved it would have the same strength as it did as a Buizel, is wrong.
Charizard wins because the writers realised that a big old fire breathing dragon is popular. In the match against Brandon, Bulbasaur was much more successful that Charizard against Dusclops, but would you claim that Bulbasaur is the stronger of the pair? I think Charmander/Charmeleon would have pulled the same things off if put in the same situations, albeit in a different way. However, they wouldn't have put it in the same positions because a big red dragon is more "cool" than a little red reptile. That difference doesn't apply to Buizel/Floatzel, as they look much the same.
Whether the anime says evolving makes a pokemon stronger doesn't mean that the writers take any notice whatsoever of it when writing battles. It's a dramatic device to emphasise the mid-battle turnaround. Their job is to make it interesting, not realistic.
The razor leaf example is fallacious. Such a thing would only be done for dramatic effect; to heighten the "are they going to escape" factor. It wouldn't have any bearing on later episodes, and if they were ordered not the evolve the pokemon, are you saying that it would therefore fail to escape the cage, and therefore be stolen? Of course it wouldn't, nothing ever gets successfully stolen; it would have succeeded just the same after a few attempts to heighten dramatic tension.
I'm not comparing two different pokemon in different evolutionary stages. I think you think I'm using the Buizel beat Floatzel argument. I never mentioned it, and indeed haven't seen the episode involved. However, let me pose you a question:
Buizel managed to beat it's evolution. Logically, if it had already evolved by that point, it should have beaten it even more easily. Now, that wouldn't have been nearly as interesting to watch, if it had been a walkover. Do you think they'd have made it a walkover anyway, to be realistic?
Of course they wouldn't. They would have him find it equally difficult/easy whether he was evolved or not. Otherwise, it wouldn't have been interesting to watch. That's the key here. The writers job is to keep it interesting, not realistic, and I think people forget that sometimes.