The determining factor is probably comparing the trigger vs just playing another 1 drop or card draw instead. Comparing it to a 1 drop, you could say that in the case of blood-priest you are paying 1 mana for the bodies, and 1 for the drain effect. That means the drain has to on average deal as much damage as simply having two more bodies in play would. There will be times where you have no other party creatures, or you have 2. A fully party is very unlikely. Let us assume then that on average you have a party of 2, which is 6 damage total.
With pump effects, your vampires will on average be 3/3s. This means that two additional bodies are offering at least a potential 6 damage, possibly more if they attack more than once. The damage potential of just playing two 1 drops instead of this card is better, but I could see the argument that blood-priest dealing direct damage is more reliable.
In the end, leaning into synergy with the number of bodies in play is probably the better direction as it is what Edgar is best at. It is much easier to optimize for a wide board than it is having a 3+ party. Blood-Priest is by no means a BAD card, but if you have a refined deck list there probably isn't anything worth cutting for it.
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With pump effects, your vampires will on average be 3/3s. This means that two additional bodies are offering at least a potential 6 damage, possibly more if they attack more than once. The damage potential of just playing two 1 drops instead of this card is better, but I could see the argument that blood-priest dealing direct damage is more reliable.
In the end, leaning into synergy with the number of bodies in play is probably the better direction as it is what Edgar is best at. It is much easier to optimize for a wide board than it is having a 3+ party. Blood-Priest is by no means a BAD card, but if you have a refined deck list there probably isn't anything worth cutting for it.