We did just chat about this 2 weeks ago.
http://www.airgunbbs.com/showthread....FWB-experiment
My own view is that, despite my liking for the Giss system, the FWB was a slightly better overall package (general quality, reliability, stock design, trigger feel, after sales support..). It’s incontrovertible that it won the most matches.
It certainly would not have hurt sales/credibility for the FWB that FWB specialised (Sport aside) in 10M target stuff, whereas Diana made everything - tinplate cheapies, pop-outs, mid-price sporters, etc.
And Diana stuck with the break-barrel 66 until they brought out the sidelever 75 in (?) 1978. Given the strong prejudice over the years against break-barrels for ultimate accuracy, that must have helped FWB too.