Shards with the description "Your primary attacks..." apply also on secondary attacks. This seems to be the case on all shards but duo to some shards not working it is hard to test for all. It is easy to spot on the "Overwhelm" and "Life Leech" shard. This can be used to "abuse" some mechanics of the spheres, like using flamethrower for squire and it heals and stuns all enemys while he still gets the benefit of blocking meanwhile. Also the secondary attacks have multiple projectiles often, and the stun from Overwhelm shard is applied to each of them, this can lead to stunlocking even bosses in C5.
Steps to reproduce:
Shards which say "Your primary attacks ..." only working on the primary attacks.