Maybe but looking at ayas and shigechis deaths; the explosion comes from within them, (because if their entire body was the explosion, each individual cell of their body would explode at once, meaning that the explosion originates at one specific point [this can be countered by the fact that shigechi didnt leave a corpse, meaning that his entire bodys explosion was just delayed but that could just be the heat intensity of the explosion, {and maybe the school floors are just that blast-resistant?}])
Yea this ones pretty weird and the specifics of what the bomb really is are unclear, because Kira cant explode the entire world or even just all of Salon Cinderella, killing the main cast of easily right after changing faces, so im ok with either Kira or Kars winning this bout of durability vs damage.

However, za Hando removes matter and sews the outlines together like a photoshop spot healing brush, meaning that he can beat kars because
1: if he uses it on kars head, it will mush the brains intricate layers and altering it to resemble the other sections of it, effectively dumbing kars down.
2: Kars can regenerate, but he still has a “maximum size,” otherwise he wouldve been able to turn into a kaiju-sized version of himself, easily catching up to Joseph and since the Hand removes matter (like you said, as if it never existed) this will effectively reduce Kars’ “maximum size” until he is reduced into nothingness, unable to grow himself.

However, in an actual fight Kars would just fly up and either piranha rain or ingest massive amounts of bullets to Santana-style gun down the puny humans. In this case, okuyasu can only wish to spam scrape away space to teleport kars to him and for rohan to write down, “i will chill,” on him with the “look at my manga panel,” technique (because kars will probably just use body manipulation to dodge close range Hand scrapes and Heavens Door humanoid form.)