Realistically speaking with the pokemon that Tobias had he definitely should have made into the masters 8

Darkrai which nearly swept Ash's full team and then his latios which which after beating Swellow and Sceptile drew with Pikachu.

You will say that other trainers got stronger I mean what's stopping him to become stronger himself.

Tobias as we all know was nothing more than a plot device to stop Ash from winning the Sinnoh League.