User blog comment:B214/Volume 22 spoilers/@comment-28087053-20170114184806/@comment-29963364-20170123215853

We also should consider that when Azazel (and later Ajuka) asked Shiva to do something about Trihexa (if he could), they had no idea that Trihexa had been enhanced by the Sephiroth Graal.

They didn't know it would have


 * Super Regeneration (on top of already being near indestructable).


 * Scale Mail Mass-Production.


 * Able to split its' body into 7 (only slightly less powerful) bodies.


 * Able to eject its' consciousness to continue fighting.

If Shiva thought he couldn't "definitively" win against Trihexa before he knew about these abilities, then he absolutely couldn't win.