I'm not too knowledgeable about Dominion since I've played very few games (and none since I understood the 4-1 or tentative 3-2 meta) but I feel that having the buff be only up if you hold both points would be worse...
My assumption is based on :
1) It is possible to snowball in Dominion
2) Revive is commonly used in Dominion since it allows you to come back from a blunder.
2.5) A blunder in Dominion can create a huge turn in power.
So basically, since it is possible to snowball on Dominion, you have to rely on blunders/nice plays to make a turn in power. Revive inhibits the possibility of coming back, while keeping it extremely plausible (9min cd).
With that said, Having to hold both positions really makes it more snowbally since the team who has the advantage at any given time should have more Control Points, making it easier for them to capture the target while defending their (they can sacrifice 1 top/bot for the objective, making it that the 2/3 is still present but rotated). Once they have the buff, they will snowball harder since they are more powerful (basically a baron effect). Also, the underdog team has much lesser chances to get the buff since they then have to capture 2 different CPs within 1 counter-push and revive+buff helps the leading team balance out their blunder...
Still, like I said, this is all theory crafting and 1 thing I'm not quite sure but I assumed would be true while it might be wrong is that most matches will have 1 team advantaged (like in all mode) and that this team will have half of the time a lead big enough that you can't really catch it all back and become the one with the advantage with only 1 good play. Or basically, to translate it in simpler terms, if I understood Dominion right (by thinking it is a standard game mode...), most leading team will usually snowball to a 5-10k lead while a counter play will give ~5k bonus (i expressed it in gold because expressing in power is very... awkward), meaning that you will usually need 2-3 good plays to go from underdog to advantaged.