MCP is great, but it adds a lot of extra latency. The MCP servers themselves will stuff your context full of tool details, taking up valuable tokens that could be spent on code context. Then at runtime the LLM has to decide to call a tool, the tool call has to come back to your machine, the data is gathered and sent back to the LLM, then the LLM can act on that data. Multiply this by however many rounds of tool use the LLM decides it needs prior to taking action. If you are lucky the LLM will do a single round of parallel tool use, but not always.

The advantage of something more purpose built for gathering context from the IDE is that you can skip a lot of roundtrips. Knowing the user's intent upfront, the IDE can gather all the necessary context data preemptively, filter it down to a token efficient representation of just the relevant stuff, add it in the context preemptively along with the user's prompt, and there is a single trip to the LLM before the LLM gets to work.

But yeah I agree with your point about CLI capabilities for running in parallel, integrating in other places. There is totally room for both, I just think that when it comes to authoring code in the flow, the IDE approach feels a bit smoother to me.