That guy is Bart de Zwart. this is his blog:
sup-crossing.blogspot.com/I,m by far not as good or fast as Bart, On the Battle of the coast, a Dutch beachrace, he litteraly put me on a lap on a 5laps race

so I don,t doubt his knowledge but its IMO its just an opinion very location based.
Last autumn i did my first Maui trip (1month ) and it really suprissed me predicatble breaks with channels etc etc are and how fast the waves travel overthere. Most of the guys paddle a bit faster rockered and bigger boards. In those conditions a smaller blade and a higher cadence makes sense. The 8.5pro I paddled overthere was called very small and short for my 90kg. Because the waves run longer and are bigger they don,t need to turn very tight and they can catch waves with there longer boards with less effort so a smaller blade with a very stiff overthere, make sense...but that is Maui,
At Maui I paddled most of the time the smallest Starboard paddle and my Kialua ShakaPuu
At home in Europe we have mainly beachbreaks the good guys paddle rather smaller boards and with those combined with the shorter period between the waves and the total lack of channels (at my homespots in the Netherlands we call 5secconds a long period and headhigh a big day :)) a bigger blade (but with a softer saft adding comfort) can help you to wrestle your way faster through the white water of all the waves coming constantly in, as well pulling you on a wave on a sub 8ft sup.
@Home the ShakaPuu is often a bit small for me and I prever my Ke Nalu Maliko with Xtuff-S shaft and my wooden Malama.
For Racing both flatwater on a 14ft and beachraces on a 12.6 I prever my Quickblade Magic90