Taint seeds right now are just a nuisance and not a real threat. Some small buffs could help. I would suggest to buff the health and make taint seeds spread the tainted lands biome. Also making the seeds more resistant to ranged damage or competely immune to normal damage could be considered. That way the ethereal blooms could be implemented to damage the seeds and revert the biome.

If this doesn't fit the mods theme, this could be implemented in the TC6 fix addon that was mentioned.

Taint seeds are notorius for spawing in blocks and just suffocating. They spawning pattern thay have could be improved or make them outright break blocks similiar to the wither.