I wonder if the Lance Era has distorted views on this? He gives the impression that you need 6 sacrificial mountain-goats to do well in the mountains. I'm not convinced this is the case, but I haven't really paid much attention to the domestiques of recent winners.
A better analysis might be:
of teams that had a strong contender for Yellow and Green, how did they get on?
Maybe few teams have bothered employing 2 such people in the recent era.
It feels like your team isn't critical in the mountains - the sprinters just drag themselves round in the time limits, the GC contenders just need a massive engine and they'll do OK! On the flat stages, the same team that gets your sprinter to the last 10km in safety would also be good at getting your GC guy there. I think.