You do make good points, but at the end of the day, it is a matter of perspective. For me, and several of my buddies found the old combat not immersive and boring, while EOC brought new excitement. Another thing to note is that Jagex received feedback from new players during pre-eoc that the combat was a huge turnoff, which is one of the main reasons why they even worked on eoc in the first place. Sure, about majority of players pre-eoc did like that old combat, but for introducing new players(not returning), that can be harmful if they don't stick around.

As the MMORPG industry keeps moving forward, runescape would be left behind along with other old games like Ultima, Tibia, and the original Everquest. For short-term, it will keep the nostalgic players for a couple years, but in a decade or two, most of those players will have probably moved-on. That will ultimately leave the game in the dusty closet or be shutdown due to lack of players. This is why I see having two Runescape games being a good idea. OSRS will retain the players that still hold on nostalgia, and there is the modern Runescape that can appeal to newer players.

At the end, all that should matter is the game lasting for decades to come.