It's a heavy-duty SLX essentially - which makes it sort of parallel to XT but in a different direction (more DH,less XC). I've used/got a few 9-Sp components.
Weight wise I don't know about the full range, but shifters are very light and shift VERY rapidly, like XTR of a few years back (guessing the internals are essentially the same).
Mechs are tricky as much of what's around is shorter cages as it's 1-ring/DH specific, no no good for a triple-ring setup.
If you're comparing Saint (M800/810) to older XT or lower, you won't notice them being heavier that's for sure! I think the cranks are the heaviest 'over-engineered' part, but it does depend on what you're riding and how you ride.
Saint brakes probably unnecessary for XC (weight and price-heavy), but the rest of the shifting kit is absolutely fine, it works well in mud grit & gloop as well, and you won't feel worried about breaking it!