R5s have always sounded pretty boring. When s2000 started becoming the new group N in the late noughties, the sport exploded. IRC grew and grew, and I'd say overtook the WRC. The cars obviously had slighty better performance than group N subarus and mitsubishis, but when you stood in a forest there was a world of difference.

The 17 cars and now the rally1s have the pure spectacle, can hear them from miles away and also have the speed. R5s don't have the spectacle to be the top class without big tweaks. S2000s would've done back in the early 2010s, and that was reflected by how strong the IRC was and how many fans watched / attended.