The core pipewire package is required by OBS and Telegram so cannot be removed
But PipeWire systemd socket & service can be disabled/masked to continue using PulseAudio, as already mentioned in OP
(replacement package pipewire-dummy from AUR works with OBS but not with Telegram)
I suggest adding additional options to module-echo-cancel configuration to force use of 2 stereo channels, either channels=2 and/or use_master_format=1
If audio is still not working as expected, check PulseAudio configuration with pacmd dump