There hasn't been a engine on the market to give a chance to prove itself. I know on a cost/hp an LS is tough to beat given the simplicity, reliability and robust aftermarket it has, but you would figure by now someone (Other than Mercury) would have prototyped something.
The Boss 9 isnt DOHC, it is a semi-hemi I believe.
Interesting that the design of the engines I worked on back when I was just a lad in the late 60’s early 70’s is making an apparent come-back... I worked on Fairbanks-Morse and Waukesha 2 stroke diesels that were built in the 40’s that had dual crankshafts and no cylinder heads. Massive power at low RPM.