Post-game, they're not all exactly level 60, but they start at level 50ish. It basically means that you have first forms with really strong, but sometimes baffling, attacks (Hydro Pump/Earth Power Poliwag, anyone?)
The mix of super strong attacks and paper thin defences means you get one shot really easily and the high levels mean it takes a long time to grind a level to evolve your mons. The answer might be to use candy on the new catches so you have easy access to their less shit forms.
Is this a long-winded of saying I may have ragequit and lost all my progress after the indignity of being taken out by a fucking Brave Bird spamming Squawkabilly? Maybe_so.gif. Fuck you, Tomo the Courier, neither you or your birds will be seeing heaven.