Yes, those are heavy basses. I play the ESP LTD D5 and she is a beast. Few times my shoulder would hurt after a few hours of standing and playing.
I have not had that issue at all with mine. I did have to get a compressor to help pull in the higher strings so the sound was a bit more even across all strings.
I also string my different - I pull off the low B STring and string it with a high C instead.
I would have it looked at, just so you are without a doubt correct in what you think the problem is.
I'm a bass player. I don't get the love at the shows, but I hold the rhythm section down!