Believe it or not, I came here in the first place to confirm you were indeed supposed to loose against him.
I'm on my first run, I didn't know at all I'd encounter a lv. 75 Garchomp I was supposed to loose against, so I didn't prepare anything, and I beat him on first attempt. ^^'
How ? With a lucky Curse, because he missed my Cofagrigus ^^' Then a Sturdy Forretress + Self-destruct to speed up the process a bit, and just stalling.
I assumed you were supposed to loose against it because at the end of the fight, things happened as if I had lost - and by logic anyway, no way you can ask a player to beat this at this point of the game with pokemon under lv. 45 *_*
Well now I know I was supposed to loose. Guess I'm not one to do as I'm said.