So I know this is a stupid question, but since I first started playing pokemon as a kid in 98, I've always just overleveled my starter and torn through all opposition with him alone.

Then XY/ORAS came out and had full party exp share and I started raising full teams and loving it, to the point that I dont want to play the older games because I'll miss having a full team of useful mons.

So my question is this: how do you effectively level an entire team in the older gens? Is it just mass slaughtering of wild mons or is there something I'm missing?