In reply to Clauso:
re massive weight difference:
belayer will fly - they may be happy with this.
soft catch - you'll get one.
getting wiped into the wall might be uncomfortable,
coming into contact with the 1st clip/runner sounds nasty (although not known this personally)
anchor:
anything that assists is helpful, even it's weak / only adds some general ballast
ground anchor positioning is rarely ideal - however you can be usually be very flexible in positioning if all you need is a bit of extra assistance / flight control.
i.e. having a ground anchor a good few meters back from where you stand will still help: allows some vertical load to be transferred / stops belayer flying horizontally / minimizes uplift....
re falling rock:
this can be managed - location of where you stand, and freedom of movement in the system (not necessary to be pinned to one spot).
having slack in the anchor is ok - you'll still minimize belayer flight (travel through air - not running away)
how much freedom of movement do you think you need - to a certain extent you're already limited in movement by the climbing rope and the terrain you're on.
stuff falls fast and will bounce randomly in any direction - looking up reduces the effectiveness of your helmet (bye bye sweet high cheekbones...)
worth discussing options with belayer; make sure they're happy
I'd suggest that the person in sole charge of operating the single mechanism that stands between yourself and extreme pain / terminal death (the worst kind) should be comfortable in what they do.... (and know what to expect if they do and don't use ground anchor)