Much earlier, I tried to set up some static analysis tools so that the coding agent would have access to dataflow analysis etc. tools instead of just grep for typed python. If there were benefits, they weren't easily apparent :(

Which one specifically? The ones I found looked like unmaintained throw-away experiments.

I haven't tried it since it was first released but it didn't seem to work at all for me back then.

It was so slow that the roslyn results would be lagged well behind any edits it was making, which would just leave it confused.

I don't think they're comparable. RTK just modifies the output of CLI tools to reduce the number of tokens, a Roslyn MCP gives the agent a fundamentally superior way of interacting with a C# codebase.