DX11 against DX9 has to be viewed from the point of a platform strategy. If an engine has to be cross-platform, then it makes sense to stick to DX9 as long as the next consoles generation appears. But if you have a technology based on Windows only then by all means, DX11 is a big improvement. You never can have almost unlimited lights with the current forward renderer. And DX9 implementations of deferred rendering are often too slow.

DX11 not only gives you tesselation, it can give you freedom where you can have much faster rendering, more lights and post-processing at almost no costs. It can be an advantage on Windows systems.

Of course many current games do not come with such modern technology because pc sales are only 10-20 percent of all sales. Consoles are more important. But a PC-only engine could use this situation as chance to fill a gap.