Hmm... That's a really hard nerf. It drastically changes clan fighting tactics.
Clan 'mechs will have to avoid the brawl; we will no longer have the equipment for it. And we can't modify our battlemechs' engines, so no standard engine zombies on clan side. I figure this will probably shift the meta more toward cover-sniping even more.
You know, IS 'mechs get the choice of engine. If you want to put an XL engine in your Jagermech, well, you know the risks - you can't brawl because a single side-torso shot will kill you.
- @russ_bullock Or Betty spams you with "Recalibrating Engine" for 10 seconds while you enjoy a 90% reduction in speed and heat dissipation.
If a side-torso loss is basically ten whole seconds of being completely useless in combat, clan XL engines become just as bad as IS engines - that ten second debuff will virtually assure that the 'mech in question dies very, very shortly. Unless they were already really close to cover, which probably encourages the cowardice meta, unfortunately.
On the other hand, if clan 'mechs could survive with both STs down, this could be neat. I think it would probably still be a nerf overall, but a little less severe of a nerf, and one that gives more playstyle options.