Agree completely. For the 2018 Rams it made sense. The 2019 and 2020 Rams may be a different story. If the Rams project two new starting OL they'd likely play (with Goff) more next August. Etc.
For some teams it's the right approach. If you have a new HC, new QB, young defense, etc. it is not.
Also factor in the joint practices with other teams thing. I'm a big proponent of them and even believe 1-2 preseason games should be replaced by controlled scrimmages with other teams (in stadiums with paid attendance- though at a much lower cost). McVay believed, rightly in my opinion, that the two days with the Ravens equated to at least one preseason outing.
Being in southern California I believe the Rams should have joint practices with the Chargers and/or Cowboys every year.
There was some rust Monday Night- especially in the Rams passing game. It was a trade off they were willing to make.