Will agree that what you say concerning plywwod shelf end-joinery has merit to it...theoretically. However, I've never had a delam failure or weakness/sagging in a ply shelf from doing things the way I suggested. That's no failures in say 35 years or so.
But yes...with the quality of plywood seemingly continuing to degrade...delamination may become more of an issue.
Fact is that I choose from the many different end-joinery options depending upon various factors including whether a plywood, composition board or solid wood is being used for the shelves....and depending upon upon how deep the shelves are, how long they are and what they will be used to display/hold.
Frequently enough, I will choose to rabbet both sides of the shelf end a bit ( 1/4" - 3/16") instead of just one side. Sometimes I've used french sliding dovetail joinery. Sometimes those DTs have been "run thru" at the front of the standards to show off the joinery (at the client's request) and
other times the joinery is completely hidden from the front side.
The reason behind describing what I did was just to pass on the notion that a joint with at least one shoulder will result in a stronger end result than a shelf simply fully inserted into a dado....as that is a structurally weak
way to put things together which are "free-standing".
The simple "single shouldered" joint can be particularly useful in getting a clean look if someone makes up their shelf standards from solid stock. Reason being that frequently enough they may be lacking a surfacer to smooth the interior surface of these glued-up standards to achieve a perfectly flat side. Instead, they may find themselves sanding that surface
and the odds of getting a perfectly flat interior standard side are far less.
Consequently, there will likely be some gaps visible if a true straightedge is held up against this surface once the sanding is complete. Inserting the tongue of the rabbeted into the dado such that the shoulder is down (actually I should have said..on the side that is "away" from the normal angle of view) does not show off or reveal this gapsiosis on that side of the shelf, although presenting the straight-edged
shoulder of the rabbet would. IOW, the end result on the "show side" of the shelf is then more pleasing to the eye...and far less bruising to the builder's ego every time he/she looks at the piece.