Let me see if I got your intended message correct.
It is possible to profit from trading ZF outright perhaps by day trading or scalping.
IT is also possible to profit from trading spread (ZF - ZN) through swing trading.
Price movement will probably be gentle.
Margin needed will be smaller. So generally traders trade in greater volume.
Hope I am correct.
Generally speaking, your points are fair. There are plenty of proprietary futures traders in Chicago, NYC, London, Sydney, Singapore who day trade inter and intra market spreads (for stupid size typically), but they have the significant advantage of Member Clearing rates and just a few cents in brokerage (GCM) commissions. At retail clearing rates day trading spreads other than the more volatile ones would not make much sense. But swing trading futures spreads on retail clearing/commission rates makes plenty of sense. For me personally, my trade holding time frame is entirely dependent upon a particular spread's volatility. I could hold a Eurodollar Butterfly for six months, and an ICE GasOil/Brent Crack for two days.
Keep in mind that there are literally thousands of regulated electronic exchange recognized potential spread combinations. It can be a very appealing proposition for the type of person who might not necessarily want to follow the herd. Spread strategies can have quite a bit of dimensionality to them, and typically appeal to creative thinkers.
Yes, the price movement and volatility - particularly for exchange supported intra market spreads, will be much better behaved than the analog outright prompt futures month contract.
This is especially true for intra market spreads if you stay away from the first three months in the curve where spec order flows dominate the volume.
So yes, depending upon the individual it might make sense to consider the possibility of levering a more tamed price action versus the idea of trading smaller size with outright futures contracts in a much more volatile and choppy price action scenario.
If you can manage to query some proprietary firm futures traders in Chicago, NYC, London, Sydney, Singapore I think you'll find that the majority of the big earners are indeed employing some type of spread trade strategy. Nearly all of them will carry a core position overnight and massively day trade around it during peak market hours.