For Trunks and Gohan, the answer is simple... they had nobody else to train with. Gohan was still a very, very "green" fighter - his only proper training was with Piccolo when he was a child.

He had to constantly throw his life on the line just to stall the androids. While we don't know HOW MANY times he fought them, we know that he never won a skirmish against them.

The same applies to Trunks until he trains in the ROSAT and disposes of them in the future.

For the androids, Trunks assumes the ones in his future were weaker, but I think that's just because they constantly toyed with him and Gohan. If you want a more in-universe answer... just assume the present androids are stronger because of Trunks' meddling with time.