Patent trolls: I don't have a good answer, other than (1) nobody would be worse off than before in this regard, and (2) once the only lawsuits are from patent trolls, it may be much easier to enact legal change. (Members of the pool will be incentivized to lobby for patent reform, rather than preserving the status quo).

Small developers: They just join the pool, or don't join and just don't sue anyone. Members in the pool would irrevocably sign away their rights to offensive lawsuits, so how could it turn bad? In other words, the "stash of legal power" is not concentrated by "competitors", but by "we, the people".