After gaining a cpl, any time spent as an endorsed co-pilot is time well spent.Especially if you are with another who is prepared to share his knowledge. Not always the case though.Some begrudge a newbie being next to them.
The problem comes when is it time to move on ? ,to a single engine single pilot envoirnment.Away from the shelter of the 2 pilot 2 engine thing.
You will still need command hours for an ATPL.
There is no easy road just hard graft.