He'd be much easier the first time around for sure.
He could have Kangaskhan or Taillow with Scrappy to deal with Ghosts, but a single ghost pokemon would be quite a hard counter to the team. Level 1 pokemon with Prankster could add another dimension to this team.
On the flip side, it would be cool to see an early game trainer with level 100 pokemon that's still easy to beat with the right pokemon. A level 100 Shedinja or Ditto isn't particularly hard to counter.
Level 100 Shedinja would out-speed and OHKO your entire team early game. It would be fun if it was a perma-sand route though, but dat experience....maybe make it level 30.
Level 100 Ditto would be VERY fun though, but it would need a lower level so your mon doesnt gets a ridiculously high amount of experience though.