The only really relevant target I can think of that FB hits better is Tapu Koko. Genesect is OHKOd by punch, phero is OHKOd by anything, oh wait just calc'ed that you also get an OHKO on bulky magnezone with blitz that punch doesn't get, but overall, there's just not enough reason to use blitz outside of 'do more damage.' Admittedly, 'do more damage' is a v good thing on a tank, but your tank stops being a tank when it can't, well, tank, which blitz prevents. For example, if you come in with rocks up and OHKO tapu koko with blitz, good luck coming in again (not that koko is staying in anyway).
Also, shadow bone is the move you click the most, tbh my experience with alowak is like, 8 Shadow Bone for every 2 Fire STAB for every 1 Ground coverage. And the fire STAB is only used for SE hits and normal types.
Also also, you shouldn't be running max attack alowak unless it's on TR.
You haven't listed a single relevant defensive threat.
252+ Atk Thick Club Marowak-Alola Flare Blitz vs. 248 HP / 96+ Def Thick Fat Venusaur-Mega: 218-260 (60 - 71.6%) -- guaranteed 2HKO
252+ Atk Thick Club Marowak-Alola Fire Punch vs. 248 HP / 96+ Def Thick Fat Venusaur-Mega: 138-164 (38 - 45.1%) -- guaranteed 3HKO
252+ Atk Thick Club Marowak-Alola Shadow Bone vs. 248 HP / 96+ Def Venusaur-Mega: 154-183 (42.4 - 50.4%) -- 1.2% chance to 2HKO
252+ Atk Thick Club Marowak-Alola Flare Blitz vs. 252 HP / 144+ Def Hippowdon: 217-256 (51.6 - 60.9%) -- 94.1% chance to 2HKO after Leftovers recovery
252+ Atk Thick Club Marowak-Alola Shadow Bone vs. 252 HP / 144+ Def Hippowdon: 153-181 (36.4 - 43%) -- 98.2% chance to 3HKO after Leftovers recovery
-1 252+ Atk Thick Club Marowak-Alola Flare Blitz vs. 248 HP / 244+ Def Landorus-Therian: 160-190 (41.9 - 49.8%) -- 90.6% chance to 2HKO after Stealth Rock
-1 252+ Atk Thick Club Marowak-Alola Shadow Bone vs. 248 HP / 244+ Def Landorus-Therian: 114-135 (29.9 - 35.4%) -- guaranteed 3HKO after Stealth Rock
Without Flare Blitz, you get stopped by Mega Venusaur, Hippowdon, and Landorus-T. You know,
actual defensive threats.
Hell, you even struggle against Chansey.
252+ Atk Thick Club Marowak-Alola Fire Punch vs. 4 HP / 252+ Def Eviolite Chansey: 258-304 (40.1 - 47.3%) -- 47.7% chance to 2HKO after Stealth Rock