But it wouldn't make sense to only change tutor Echos, and the other three don't really deserve a nerf imo.
I'm not so sure about that. Of course, after the nerf the provision cost of these tutors or other echo cards should be adjusted accordingly, maiking them available for less points.
Fortunately, we can use a bit of creativity in order to make them "weaker" on second use.
Some ideas:
Blood Eagle
1st use: current effect, draw a Warrior unit up to provision 8, any warrior at Bloodthrist 3
2nd use: draw a Warrior unit up to provision 8, any warrior at Bloodthirst 5
Coup de Grace
1st use: current effect, 3 dmg
2nd use: current effect, 1 dmg
Dies Irae
1st use: current effect
2nd use: only boost Firesworn units
Ard Gaeth
1st use: 4 turn effect on both rows
2nd use: 3 turn effect on both rows