Can't believe people struggle-on buying more and more Shimano derailleurs. I went through this years ago, finally realised that the parallelogram links are super weak and bend, which makes the cage point in towards the spokes and then catch and destroy everything. Switched to SRAM and found a different set of problems, the cheaper chains and cassettes (GX and below) work great for a while but wear out super fast. XO stuff seems incredibly tough and long lasting. I've got huge gouges in my XO derailleur on the bike now from multiple hits and scrapes but it still works really well. I've only destroyed one XO mech in the last 5 years or so and that was from a stick that got caught and bent the cage. Everything up top was fine. Been through several derailleur hangers too.
I used to really like Shimano, their HollowTec2 cranks are undoubtedly fantastic, but the sad truth is that they just can't seem to make a decent rear derailleur. Even the DH stuff like Saint and Zee was piss weak.
Switch to SRAM XO, wax your chain and keep on top of re-waxing and rotation and although the initial investment is high the total cost (and hassle) of ownership is way lower. The cost of the cassettes is really hard to take but you do save weight too.
Not tried the non-electronic transmission stuff yet but I suspect that that will be good too as long as you shell out for the more expensive one.