You do make some good points. But, the Primus line isn't exactly a slouch in the bass department either.
I think that if it were my HT, I would probably take your advice and invest in a ~$1k sub first and see where that got me.
I think I would be fine with Primus for my HT, but I would want something overall better for a dedicated music rig.
My P363 don't get much use, likely these will become a workshop speaker whenever I finally get a dedicated workshop. They are OK, but when you stack them up against my GE T2 or my Alexis-Philharmonitors, it's no contest.