gtfs-realtime-bindings-php | Provides PHP classes | Networking library

Yes, your assessment is correct. gtfs-realtime-bindings requires centraldesktop/protobuf-php:0.5.* which has an unfortunate requirement on symfony/console. In later version they changed it to be a dev-requirement only (even then only console 3.x).

I don't think you can downgrade your symfony/console version safely. Instead what I would do is create a Pull Request to gtfs-realtime-bindings that bumps the minimum required version of centraldesktop/protobuf-php to ^1.0. This might require other changes to the code as there might have been breaking changes between 0.5 to 1.0. Unfortunately centraldesktop/Protobuf-PHP does not provide an upgrade guide, so you have to figure out if anything breaks via tests or code inspections in your IDE. Luckily gtfs-realtime-bindings is tested and seems to be rather small, so it should be manageable to do this upgrade even if you don't know all the internals. Plus, when you open a pull request that is work in progress maintainers will likely support you.

Another option would be to search for alternative implementations of the bindings or writing your own.