Anyway, ultimately you have to decide how much you want to comit into dealing with characters.
That's the point I'm having with points cost and unit size - sure, I can take more snipers, but then I can take less of anything else. Last game, I faced biker captain/libbys with storm shields. Wounds on 5+, saves on 3+, so it would take 12 Eliminators to kill a single captain in 2 rounds, which depends on 5s and 6s to wound, and almost half of the calculated damage is just MWs/6s. Sure, with lucky shots 1x3 eliminators could theoretically kill the guy in a single round, but that's just bringing a knife to a gun fight and hoping for the other guy to be out of ammo.
A fully loaded biker captain is a 121p model, the 12 eliminators currently cost 288p. When I'm just fishing for 5s or 6s, that's just too many points. If they get closer to stalker intercessors I'd reconsider, but right now I don't consider them effective at their job. Useful (mostly for their psychological impact, as mentioned in this thread several times), but not worth their points in something beyond fun games or games where you know your opponent will bring T3 characters. For serious character sniping, a vindicare should be both a greater, longer-ranged threat and more effective at his job, at just 13p above 1x3 eliminators.
Currently, IMO the best Astartes character deterrent is the phobos libby. Limited range, but can target characters (even in CC) with up to 2 MW per round (exchanging hit/wound/save rolls for a roll with warp charge 6), halves movement and potentially generates CP in the process, while being a protected character in turn and ignoring falling back. Every time I've used that guy, he has had serious impact on how my opponent deployed his characters - if their super fast character runs into a screen and can't get out of range again, it's in deep trouble. Halving the movement means chances are you can repeat the process next round and maybe switch to Smite for more MWs. Sure, sometimes the movement debuff is needed somewhere else, but the possibility of it is what my opponents feared most.