sub-sonic doesn't really need a flying tail to retain control authority but once you get into trans-sonic/ supersonic regime then the ability to trim mach on the stab leaving full authority on the elevator becomes useful.
Hoppy, a THS doesn't really give you access to supersonic.
Once you are supersonic, the significant aft shift in CP (Center of Pressure) requires significantly more nose up
right now than a slow moving trimable stabilizer can promptly deliver. For that reason, full flying slab tails are the preferred means of control once supersonic. That reason and flutter are the primary speed limiting factors on our modern THS equipped airline flying machines.
Even the Korean war vintage F-9 Cougar switched pitch control method once gear up to a full flying tail with the elevator locked in line with the HS, and it could only reach supersonic in a vertical dive.
