In fact, there were not much air force around the world that was actually able to afford any kind of "hi" fighter in the first place, and of those who could actually afford a hi fighter, not all went with the hi-lo force structure (especially the Europeans).
Also, USAF, the founders of hi-lo force structure themselves, slowly moved away from the idea ever since the F-16 became a multi-role workhorse fighter. This is especially true with current F-35, which at its inception was meant to be a lo fighter that supplements F-22 and replace F-16, A-10, Harrier etc but is now even replacing some F-15s, became an omnipotent fighter with humungous cost, it really isn't much of a "lo" fighter any more it seems.
Turkiye for one never had a hi fighter before MMU and for that, one could call MMU kind of a turning point in the THK history.
I also largely agree with you about the fact that current trend is shifting from the old concept of "hi-lo" to "next gen-legacy". For one, it seems like any kind of 5th gen fighter is already inherently too expensive due to its complexity, hence the case of F-35 I've described above. A lot of the air forces around the world are going for a next gen-legacy mix, although as with hi-lo mix, not all of them are following the trend (Australia and smaller European countries like Finland, Belgium etc are just phasing out their legacy fighters all together in favor of F-35).