The biggest problems with gRPC are:
- Very complicated. Way more complexity than you want in most cases.
- Depends on HTTP 2. I've seen people who weren't even doing web stuff reach for gRPC, and now boom you have a web server in your stack for now reason. Compare to Thrift which properly separates out encodings, transports, etc.
- Doesn't work from the web. There are actually two modifications to gRPC to make it work on the web which means you have three different incompatible versions of gRPC with different feature sets. IIRC some of them require setting up complex proxies, some don't support streaming calls, ugh. Total mess.
Plain HTTP can be type safe. Just publish JSON schema or Typespec files or even use Protobuf.