What time period is this in? I am 6'5 and 270...and over a year period. What you have gone through is not unreasonable for example. You like have strong legs and with the weight a lot of torque. (although a properly built wheel should easily take most of what a person can throw at it. I can do 5 footers and don't go through 25 spokes
)
Either that or your lbs is scamming you. Going through deraileurs is hard without first breaking a deraileur hanger. And for him to mention saint seems ridiculous. That is extremely overpriced and meant for serious banging (freeriding)...what exactly was wrong with your deraileurs...chains and cogs are easy to go through, I tend to go through them faster because I am not the best pedaller through rought stuff.
Rear wheel...25 spokes...at various times?A competant mech should have told you to buy a new rear wheel, handbuilt on a heavier rim. Either that or a complete rebuild. Once you break a few spokes you can very rarely FIX the problem. What rims were you running.
It sounds like your shop a) doesn't know how to deal with heavier riders and their needs and b) does know how to deal with breakages similar to fr usage.
So lets start there.