I would (only) go full spr support if I would go priest 3 -> kabba2 or oracle1/2/3, since they don’t have any nice INT scaling skills.
Repost spr vs int, lvl 15 blessing, start at +170 due to blessing base and attribute.
Int, with magic skills, at rank 7:
you get +625 magic attack, and +345 blessing damage. Total of +970 damage for yourself.
Party gets +345 blessing per member, total of +1380 (with 4 members).
With spr at rank 7, 501 bless damage for your party, and 501 for you. Loss of 470 damage for yourself vs full int.
Gain of +150 damage for each party member, total of +600 gain for 4 party members vs int. SPR-Total party bonus +2000 (with 4 party members).
Disregarding attribute enhance for int magical bonus, ignoring other spr scaling (status resistance, sp, stone skin):
Int blessing -> you +970, 4-member party +1380 => total +2350
spr blessing -> you +500, 4-member party +2000 => total +2500
For dps:
You are able to dps too, so if you are a dps build (hybrid priest), int will increase overall party damage more (with %enhance attributes).
If you lack dps skills, spr will be better for party dps, so full support => spr.
I have only seen priest3 - X - druids as dps (int), and of course priest 3 into plague doc.
on topic
If I would be a very selfish inquis, I would maximize burst damage through
priest1 (monstrance), diev1 (CD statue), pala3 (conviction), Plague doc (immunity) or monk1 (or cler2), inquis (max god smash, max wheel, 1 malleus, save points for inquis2). I really cannot drop cleric 2 though, too many good points at cler2.