Sure, but even 128kbps is about 1MB/minute, so still "a few MB per track".
I just checked a few of my latest CD rips. The FLAC rip is 9-10x as large as the Opus 128bit files. One EP was 338MB as FLAC and 33.1MB as Opus.
On the go, the listening environment is far from perfect, so Opus is fine. I still want the FLAC files on my NAS as an archive or for listening in a better environment in my home.
You have to know what to listen for, and even if you do, why should you care? It's a small price to pay for being able to store several times as much music on your phone, or for saving on bandwidth while streaming.