I agree that there are downsides to this approach. NVIDIA OpenShell does the same thing: https://docs.nvidia.com/openshell/latest/sandboxes/manage-pr.... I had wondered how they deal with the fact that client programs sometimes come with their own CA bundles. Turns out OpenShell sets various common environment variables (like REQUESTS_CA_BUNDLE used by Python's requests) to try to convince as many clients as possible that the proxy's certificate is to be trusted :) I would assume exe.dev does something similar.
(I was interested in this because I was actually working on something similar recently: https://github.com/imbue-ai/latchkey. To avoid the certificates issue, this library uses a gateway approach instead of a proxy, i.e. clients call endpoints like "http(s)://gateway.url:port/gateway/https://api.github.com/..." which can be effectively hidden behind the "latchkey curl" invocation.)
I think that a curl wrapper could serve as a universal integration with arbitrary services (as long as they have a public API), saving you a lot of setup complexity and context space. Authentication is the hard part; ideally, you shouldn't even need an OAuth intermediary. Which I think is doable: https://news.ycombinator.com/item?id=46876636. It's still a bit of an experiment, though.
I believe in an MCP-less future of agent-service interactions and have recently submitted this general alternative (which also supports Slack) based on curl: https://github.com/imbue-ai/latchkey
With that said, a specialized tool like this will almost certainly work better if Slack is the only service you want your agents to interact with. I like that the auth is transparent.
(I was interested in this because I was actually working on something similar recently: https://github.com/imbue-ai/latchkey. To avoid the certificates issue, this library uses a gateway approach instead of a proxy, i.e. clients call endpoints like "http(s)://gateway.url:port/gateway/https://api.github.com/..." which can be effectively hidden behind the "latchkey curl" invocation.)