As discussed in CASSANDRA-8477, we should make sure the tombstone thresholds also apply to range tombstones, since they poses the same problems than cell tombstones.
I'm not sure that changing the current behaviour in a minor release is something we can do safely. For one, some people's queries will suddenly and unexpectedly stop working, for two, it's a small, but non-trivial enough change for a minor, code-wise.
As for 3.0, should get CASSANDRA-8099 in first, assuming that it doesn't handle this already.
Either way, relabeling as 3.0 for now.
There is a bunch of places where we don't properly account for range tombstone, not just for the thresholds. Those include tracing, statistics etc... We should fix all those while we're at it so expanding the title slightly.