This is a nice idea, and admittedly I hadn't thought of it myself, but there is one major problem in the form of Imposter. The Imposter of a MG LO set is significantly weaker and easier to handle (especially considering it does not have the item). Non-Choiced Darmanitan sets thrive off having amazing coverage; replacing such a set with Intrepid Sword + Heavy-Duty Boots either greatly limits the viability of Imposter-proofing options, or forces the Darm set to drop coverage and allow it to be walled by more threats.Quick question:
Why would you use Magic Guard Life Orb when you can use Heavy Duty Boots Intrepid Sword?
The boost is retained during Dynamax, just like Life Orb, and most Prankster users are weak to at least one coverage move Darmanitan-Z packs
You are immune to passive Hail, Burn, and now hazards, so what else are you going to need to be shielded from that Magic Guard provides? Rocky Helmets? Baneful Bunkers/Spiky Shields?
The set of Wood Hammer / Icicle Crash / V-Create / Bolt Beak in a loser ‘s Team is doing less on all counts.
Power Whip can be used on Intrepid Sword sets, at 120 x 1.5 = 180 damage vs 156 (120 x 1.3 from MG Life Orb), putting it on par with Choice Band Desolate Land Solar Blade which is 125 x 1.5 = 187.5
This is an important difference since Rhydon can survive Life Orb Magic Guard:
+1 252 Atk Darmanitan-Galar Zen Power Whip vs. 252 HP / 252+ Def Eviolite Rhydon: 388-460 (93.7 - 111.1%) -- 62.5% chance to OHKO
252 Atk Choice Band Darmanitan-Galar Zen Solar Blade vs. 252 HP / 252+ Def Eviolite Rhydon: 408-480 (98.5 - 115.9%) -- 87.5% chance to OHKO
252 Atk Life Orb Darmanitan-Galar Zen Wood Hammer vs. 252 HP / 252+ Def Eviolite Rhydon: 338-400 (81.6 - 96.6%) -- guaranteed 2HKO
252 Atk Rhydon Earthquake vs. 248 HP / 252 Def Darmanitan-Galar Zen: 372-438 (90 - 106%) -- 37.5% chance to OHKO
It’s pretty sad when something 4x weak to a 120 base power move can live it and KO you back. Since Topsy Turvey isn’t used on Prankster very often, if at all, it seems likely that a Darmanitan-Galar-Zen will hit before it loses its boost, and that’s if the target survives what Darmanitan-Zen-Mode uses in the first place.
+1 252 Atk Darmanitan-Galar-Z Power Whip vs. 252 HP / 252 Def Tyranitar: 340-400 (84.1 - 99%) -- 75% chance to OHKO after Stealth Rock
252 Atk Life Orb Darmanitan-Galar-Z Power Whip vs. 252 HP / 252 Def Tyranitar: 294-348 (72.7 - 86.1%) -- guaranteed 2HKO after Stealth Rock
Tyranitar can secure KOs with STAB Rock in retaliation to Life Orb.
Like Life Orb, it isn’t Choice locked and can maintain a sense of bluffing Choice Band due to what Intrepid Sword sets typically use. Further, it is less vulnerable to Knock Off since lacking Power on something as frail as Darmanitan-Galar-Zen makes it more vulnerable to the other Pokemon that can survive its weaker hits. If Heavy Duty Boosts gets knocked off, it will not lose its +1 Atk, and since its already switched in before it loses it, it would need to be forced out again to take hazard damage. Offense is Darmanitan-Galar-Z’s defense, and with Intrepid Sword + Heavy Duty Boots, it has the main advantages of Magic Guard Life Orb, only with more power.
As an example, even with loser's team using one of the stronger improofs in FF Steelix, +2 Imposter is still a real threat:
+2 252 Atk Darmanitan-Galar-Zen Icicle Crash vs. 252 HP / 252+ Def Steelix: 141-166 (39.8 - 46.8%) -- guaranteed 3HKO after Leftovers recovery
To put this into perspective, with Steelix taking much closer to 50 percent now it risks being ended if it gets flinched while trying to Recover or just if it's taken some chip damage elsewhere. There's a lot more breathing room in that situation with Magic Guard which would help recover momentum more easily.
Dynamax poses an even larger threat:
+2 252 Atk Darmanitan-Galar-Zen Max Hailstorm vs. 252 HP / 252+ Def Steelix: 213-252 (60.1 - 71.1%) -- guaranteed 2HKO after Leftovers recovery
Personally I'd say the advantages aren't worth the risk/cost of trying to work around Imposter, and I often feel the same way about many Intrepid Sword sets despite their undeniable power. In general if you put Intrepid Sword on something your main concern should be whether you actually have the tools available to stomach a Dynamaxed Imposter - if the improof is breakable then the rest of the game can go sideways pretty quickly in that scenario, even though Imposter is technically the mon you have the most control over in the building phase.