I don't think Spyro is the greatest Hunter out there, but it's not the worst.
First of all, his active effect isn't the best. Although his active effect isn't the worst either. If you would compare (I'm looking at the Hunters when they are 6*s) Cowgirl Maxi and Commander Spyro's active effect, it's evident that Maxi's is a tad worse than his, but she makes up for it in her passive effect.
Spyro's passive effect: Whenever an enemy is hit by Bombardier Support, the leader's SP increases by 4 and the Enemy's decreases by the same amount. All bombs have a 50% chance of exploding twice.
Imo, even though Bombardier Support is good, it's not great. Disregarding the SP part, it states that there's only 50% of all bombs exploding twice, but it doesn't state how much damage the bombs inflict on your enemies. Because of that, I think it's safe to assume that the bombs inflict the same damage as the active effect. Because it doesn't tell me the damage that can be inflicted to the enemies, I'm assuming that a chain-1 is the same as one bomb in the passive skill.
Now, I'm not the most experienced player out there and am merely telling you what I think. But I will say that before going back to max your 4*, definitely try to max some 3* into 4* to see other heroes. More 4*, more options to choose heroes for different quests and dungeons.
Also, it might be better to wait for more responses before deciding what to do, since I'm not sure whether I'm spouting nonsense or if I'm correct.