I note that when researchers analyse some particular types of attacks on Tor security, they assume a SINGLE adversary who is capable of deploying a significant number of relays that will eventually be selected as guards and exit relays. If that is a realistic assumption to make for the purposes their analysis, then out in the real world there are probably at least three adversaries interested in attacking Tor, each of which is capable of deploying large numbers of relays for that purpose.
The interesting thing about this is that these "big" adversaries are likely to be attacking real client groups who will have very little overlap in their membership. If that assumption is true then it seems at first glance that the more "big" adversaries out their deploying relays, the smaller is the percentage of relays any one actually controls. Is that dilution effect significant?
Put another way, a client who is worried about being attacked by a particular, "big", adversary actually benefits when other "big" adversaries add large numbers of relays. It gives our client a better chance of selecting a guard NOT controlled by their adversary. It does not matter if the selected guards are controlled by other adversaries since we assume they are not interested in our client.
Is that argument too simple minded?