Seems to me that the only way to tell the difference between a dually and a single is to drive them back-to-back. Only people who have driven both are qualified to say which drives better. OTOH it only seems reasonable to think that the wider stance of a dually will be more stable than a single.
Personally I would want the best tool for the job. IMO a tall heavy 5th wheel will be more stable with a wider track vehicle pulling it, i.e. a dually. If a dually does the job better than a SRW, then you buy it. And a hitch rated for the load.
If you say you don't need a dually, and you've never driven a dually pulling a 5th wheel, then IMO you're talking through your hat. If you driven both and can honestly say that you don't need a dually, I would probably concede that you know what you're saying.