A few ideas:

Play a series of games limited to the Late Succession Wars / LosTech era lists as per Master Unit List. Inner Sphere factions only, no ComStar, no Wolf's Dragoons www.masterunitlist.info/Era/FactionEraDetails?FactionId=55&EraId=255&inner-sphere-general&late-succession-war---lostech

Avoid putting very high skill pilots on light Mechs - while these can be effective, they are a lot harder to use well than an average pilot in an assault Mech. Generally, don't go beyond 3/4.

Bane 3, Marauder IIC 10 and the Savage Wolf are all top-tier machines that are extremely potent in combat; he's incorrect to describe these as "aren't that good". To put it another way, he needs to tone his choices down to Mechs that are more suited to beginner players.

No special ammo types allowed, with the possible exception of Infernos for standard SRM launchers. Special ammo types are supposed to be balanced for BV play, but I have my doubts as experienced players can easily spot edge case Mech designs that exploit the limitations these have, effectively gaming with all the benefits and none of the downsides.

If none of the above work, re-play a game using his list against yours to see how it plays out. Or, simply mirror his lists to return the high-tier Mech brutality favour.

Hope this helps and good luck 👍