I think more trichomes is more vapor, and from what I've read sativa's tend to have less but more potent trichomes, indica's more trichomes but less potent, so the potency of both plants will be about the same, with different amount of trichomes, and thus dfferent amount of vapor
I also notice it with the harvest from last year wich I still have, 2 strains, one is more indica I think(NDB, the effect is kind of indica but it lacks the couchlock and sleepiness, wich is why I like it since I can't get high from strains with too much couchlock/sleepiness, I just get sleepy and don't notice I'm high)
the other(UK08xTyphoon) is more sativa, it does have a lot of visible trichomes but it produces less vapor and doesn't last as long in my VG as the NDB
I can't really judge the potency tough, since I haven't had the UK08xTyphoon in a while(I have less of it and since I like sativa the most I try to keep some for special ocassions), and I usually pay more attention to the kind of effect and the potency of the effect(I think most would call it the ceiling) then to the absolute potency of the weed
the NDB's effect is certainly less potent, it's a mild effect, the UK08xTyphoon can be pretty heavy in effect but it depends a bit on the ocassion(when I tried ot for the first time, when it wasn't dried yet, the effect was short but heavy, I totally lost my sense of time and when I was becoming sober again it was as if I just awoke, I had no idea how late it was or wich part of the day it was, I eventually traced it back after some thinking), but I've also had times that I didn't notice such a heave effect, with the same or bigger amount(didnt vaope much that first time since it was wet, so there goes a lot less in one bowl)