This GM sucks. He is being completely railroaded by his players. Obviously this is intentional as he is a first time GM, but jeez. If I were running this campaign, they would probably be dead and rolling up less munchkiny characters by now.

But then, if you were GM we wouldn't have One Piece to enjoy, now would we?

I think killing player characters just because they are too strong for you to handle is the trait of a truly poor DM. The DM holds nothing less then ABSOLUTE POWER, and so if dropping rocks is the most creative thing you can come up with, you're probably doing something wrong.
/Gets off soap box/ /Gets onto different one/
That said, however, I understand just how intensely frustrating it can be to be played by your players. I just believe that "blunt instrument" techniques make more enemies then friends, something I learned only through unpleasant personal experience.

I've been part of a Ponyfinder campaign, so I'm playing an Unchained Rogue Pegasus. My Dex is "insane" (it's a 22), which means I have a pretty damn good hit chance, and my rapier has Keen, meaning I can crit anywhere between 15 and 20. At the start of the campaign, this meant that, even without the Keen, I was able to KO almost any enemy with just one crit. Our GM has gotten really good at making enemies that are perfectly balanced to not be impossible, but also to not be steamrolled by our characters. It's made for some great moments, and some amazing(ly bad) jokes all around.

My two favorite jokes are both about my character, Overwatch. In the first few sessions, I could NOT get a roll higher than 10 for a Perception check, so now we've retconned that he's blind in one eye. At another early point in the game, we were asked to make a Knowledge: Geography check, which none of us had. So I said, in character: "Oh, I read it in a book once!" I rolled straight up INT, and got a Nat 20, which exploded for a total of 38. Ever since, whenever anyone (mostly me) wants to roll straight INT for a Knowledge they don't have, it's precluded by "I read it in a book once!"

that's the first boss he send out to them. if you player got killed by the first boss, there's maybe a problem.
now that he have gauged the full extent of how minmaxed their PC are, he can come up with boss adequately minmaxed.

This may be a bit railroady on the player's parts, but the GM is supposed to be the one who understands the rules the best. If the players know the rules and game better than the GM, then there's no room to change the game when you've been outplayed. RF,ED is just being a poor sport on the GM's part. Plus, the GM's gonna be getting his own back with Arlong and Smoker enventualy, nevermind the Warlords.