This is obvious advice, but can be so obvious that it just doesn't occur to people. It took me way too long to actually think "wait, hang on a minute..."
In those short stages, anything 30 seconds and below, you don't have time to evolve a Pokémon. In that case, don't waste your first slot on something which isn't super effective, just take something strong and super-effective. Basically, "optimise" is really bad on those stages because it will always place a Mega in that first slot even if it's not super-effective.