I'm pretty sure that invoking obscure rules like the original Solaris Box Set rules is a concession that the Man O' War Prime is not good.
Actually those rules came out not long after TRO 3050 did and they received a supplement in The Reaches. They also had 'Mechs in the boxed set designed specifically to use them (Juggernaut, Paladin, Onslaught, etc.), along with similar 'Mechs in The Reaches (Sasquatch, Werewolf, etc.) and they were assumed to be used in Unbound too. There was a fair bit of support for them for a while.
In one of the MoTW threads on the 3055 'Mechs, someone referenced a designer saying that the Vixen, Goshawk, and Viper were specifically designed to operate under those rules, hence the MG spam, etc. That's a lot of 'Mechs designed under that ruleset, so it's not farfetched to think that the dueling rules may have been somewhere in development when the Gargoyle Prime was invented.
Plus, they were altered and incorporated into the MechWarrior's Guide to Solaris, so they continued for a bit after it was invented too.
The Man O'War/Gargoyle Prime is indeed a beast under those rulesets, compounded by the ability in those rules for it to aim for the punch table and just let cluster shots do the work.
Then we get to the old Battletech Compendium rules where a Garg Prime could conceivably take on an entire armored company by itself (even without infernos since you couldn't use them in 6 packs back then), and could take Inferno hits for days while doing it. Infantry, including Elementals would be in a bad way too because there were no rules for reducing damage of big weapons to standard infantry and LBX Cluster shot negated Battle Armor dispersion rules.
As a note, Elementals and standard Infantry frequently used Flamers and Infernos at the time (one Elemental even used Infernos in a Bloodname duel in the Blood of Kerensky trilogy), so that could have been a reason that the oversinking was tolerated too.There were no limits on heat addition back then, and though Infernos added only turns to duration per missile, not extra heat, Flamers could do what they liked.
Not to mention that many cluster weapons combined with oversinking would have been good in a duel against an Aerospace Pilot known to use Inferno Bombs....which were pretty OP under Battletech Compendium.
Was the effect of the Prime's full loadout intentional? Dunno. There's some evidence to suggest it could have been, of course TRO 3050 was a trainwreck of bad rules, so who knows. Yes, it's bad in some situations, but there is some interesting history surrounding it.
Can the Gargoyle Prime at least be explained in some in-universe or game design context? Sure.
One bonus explanation: Maybe the Wolves expected the IS to pull no punches and break out the nukes. Nukes do happen to add lots of heat to 'Mechs at the edge of the blast. The Hoplite, which was designed during an era of nuclear warfare, is suspiciously oversinked as well.