I suspect you are dividing the dry TW by the GVWR, and are concerned that it's under 10%. Once you load a battery, LP tanks, and your gear, you will be over 10%. The trailer manufacturers design trailers a bit tongue-light, assuming you will actually put stuff in/on them.
To your actual question, I would say, "no". Any sway control system is not a substitute for proper loading. You need 10-15% on the ball. Purchasing several hundreds (or thousands in this case) of dollars worth of equipment should not matter. I'm surprised any hitch guy told you otherwise. They must have been a salesman, and not actual tech support.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller