Hi:

I typically play with the "Light Path" but now that I am trying "Dark" for the first time in quite a few years, I just realized that I'm not seeing anyone to go to for Grandmaster Blaster...so I looked up where the trainers are. Both are in Celeste.

One (Gavin) seems to be behind a locked door in Castle Lambert, and the other ("Resurrectra") only grants the skill if you kill "Tolibert" which is not something you do as part of the Dark Path, and then give the Cube to someone (which I have already given to a Dark Path minion)

Am I correct, then, that only "Light Path" party members can acquire the GM Blaster skill ?

I'd like to thank the players on this forum who answered my recent question on Monk/armor as well...that was very much appreciated.

Now, as for my next play-though attempt, I'm going to try for the first time (for me) an all-might party...no magic using skills, just to see if I can. Not sure what to expect, but I am prepping to have to get used to using a lot of scrolls for flying, water walking and the like. Should be a fun challenge.

Robert

Resurectra is one of the two Grandmaster Blaster trainers.
The other one should be Kastore in Castle Gloaming.

If the door to Kastore is locked because you stole a tapestry from the castle earlier, you might have to wait until the map respawns.

Nope, your source was wrong. Gavin teaches Grandmaster Light magic, but not GM Blaster. As fe79 said, there's a GM Blaster teacher in Celeste and one in The Pit. It is going to be rough. I ran a party of Knight, Monk, Ranger, Archer down the Light path once, and lack of decent healing sucked. If you're going magic-less, then I'm guessing you'll need to get used to resting a LOT because you won't have much other means of healing at all. The Lincoln was especially rough.

On the bright side, I was able to skip Evermorn Isle entirely since the only thing out there that mattered was Master Unarmed and Dodging. My monk just used a sword until he got a blaster.

full might kinda hard to define, if we counting archers 4 archer party is actually very strong, close to the best parties available I'd say. 4 monks isn't too shabby either really.