It was the diesel I believe, it was not a powerhouse, it might have even been the road case version, but the room was also an issue, that particular studio, while supposedly designed for proper acoustics, was very hard to get a good bass tone in those rooms. It was the late 90s too so it was a while ago. I remember sticking my wm10 on top to try to get more articulation.Which Mesa 215? The modern Powerhouse is a very different design than the old Diesel.
For whatever reason, while yes the 410HLF is an extreme example, the 410s I've played through have generally seemed less aggressive in the mids than the 15s I've played through.
Currently I play a Sunn 2000S 2x15 and it's a beast.
Really the fault was probably more the room the cab.