Some courts still allow for plenty of shot making and attacking. On indoor courts you still see offensive guys dominate because with elements like wind/humidity/sun taken out of the equation, the tennis becomes more predictable and guys who excel at hitting a flat ball have an advantage. But the modern surfaces no longer allow serve fests and 2-3 shot rallies, instead modern tennis requires a player to be a more complete player - serving your way to titles is no longer possible - in other words, even indoors you need to be strong off both wings, have good fitness, preferably have a good RoS, slice and be able to finish at the net.
Diversity? If it means guys like Isner not winning big titles, then it's something that can be sacrificed.
Indoor surfaces were fine about seven years or so ago and I didn't see any 'serve-bots' dominating.
Besides, Isner's style is unique and I like that. Shall we have 100 grinders in the top 100 who all play the same game? I'd rather see some different game styles. And Isner actually does better on higher bouncing courts cause he can actually has time to hit his forehand (on a low bouncing court he has to bend down and struggles off the ground cause of his lack of timing) and his early exits on first week Wimbledon grass testify to it. He can't handle quick, low bouncing surfaces and can't break serve.
Bercy 2010 was a nice throwback to indoor tennis when Llodra made the final with some classic serve and volley. I know you think it's prehistoric, but it was a nice change from what we usually get.