That seems clever. What about Grass Knot? Originally I had some interest in mixed Palafin to use that for Gastrodon(though that's not common anymore...and you show Dondozo is typically handled.)
On paper it looks the perfect option for clearing Dondozo, but it is not really useful. It is extremely tailored to deal with Dondozo, and doesn't accomplish much more than Boomburst. 2HKOes AV variants just like Boomburst, and only havs a 31.3% of OHKO on non-AV ones:
252+ SpA Choice Specs Tera Normal Palafin-Hero Grass Knot (120 BP) vs. 4 HP / 252 SpD Dondozo: 200-236 (88.4 - 104.4%) -- 31.3% chance to OHKO
252+ SpA Choice Specs Tera Normal Palafin-Hero Grass Knot (120 BP) vs. 4 HP / 252 SpD Assault Vest Dondozo: 136-160 (60.1 - 70.7%) -- guaranteed 2HKO
252 SpA Choice Specs Tera Normal Palafin-Hero Grass Knot (120 BP) vs. 4 HP / 252 SpD Assault Vest Dondozo: 124-146 (54.8 - 64.6%) -- guaranteed 2HKO
252 SpA Choice Specs Tera Normal Palafin-Hero Boomburst vs. 4 HP / 252 SpD Assault Vest Dondozo: 108-127 (47.7 - 56.1%) -- 84% chance to 2HKO
Sure, Grass Knot allows you to comfortably use a Naive nature if you need the extra speed without losing the ensured 2HKO, but Boomburst already has a healthy 84% chance of doing so. About Gastrodon, well, I don't know which was the standard set for it, if it preferred special or physical bulk. A full specially defensive variant, which stat-wise seems the natural way to go, is 2HKOed by either Grass Knot or Boomburst. A full physically defensive variant cannot withstand Grass Knot, true, but Boomburst still holds a 43.8% chance of accomplishing that:
252+ SpA Choice Specs Tera Normal Palafin-Hero Grass Knot (60 BP) vs. 252 HP / 252+ SpD Gastrodon: 160-192 (73.3 - 88%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Tera Normal Palafin-Hero Boomburst vs. 252 HP / 252+ SpD Gastrodon: 139-165 (63.7 - 75.6%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Tera Normal Palafin-Hero Grass Knot (60 BP) vs. 252 HP / 4 SpD Gastrodon: 228-272 (104.5 - 124.7%) -- guaranteed OHKO
252+ SpA Choice Specs Tera Normal Palafin-Hero Boomburst vs. 252 HP / 4 SpD Gastrodon: 198-234 (90.8 - 107.3%) -- 43.8% chance to OHKO
So I'm a bit skeptical of using a moveslot for Grass Knot that can be occupied by something way more useful, like Jet Punch or Wave Crash. In this regard, I mentioned Aura Sphere for Kingambit because, in that case, it really achieves something that neither Hydro Pump nor Boomburst (unless King goes tera Flying) do, which is getting the OHKO on non-AV sets and having a solid 87.5% chance on AV. Yet, I would prefer sticking to the original moves I mentioned.