This is not a bug in rclone itself, but in the install script, install.sh.
It installs files to /usr instead of to /usr/local, and it shouldn’t.
/usr (without local) is reserved for files installed by the OS installation or package manager. /usr/local and /opt were created for software that isn’t installed or managed in that way.
If you don’t honour this convention you can screw up package management.
I have patched up install.sh to do the right thing for Ubuntu. It’s easy: insert /local in all the right places. Better still: set PREFIX=/usr/local and use $PREFIX in those places.
Ideally, for Ubuntu, you’d make a PPA. My own attempts at making one (just as a test) haven’t been completed yet, but it really isn’t all that hard.
I think your concerns are unfounded: people who can run curl | sh typically have /usr/local in their $PATH, or can easily be taught how to put it in there.