Agree with you to a point.
A Lithuania type game would appear useful, for giving young players like Wilkins, Stamenic, Garbett etc a full 90 min run out. If it does end up being Belgium, Mexico, England & USA - those younger guys may just get cameo sub appearances.
Still IF these games happen Belgium and Inglerland are likely to field 2nd string sides. They already both have 6 competitive UEFA Nations League games over the Sept-Oct-Nov windows. Their first string sides don't need another game, but Martinez and Southgate would likely want to give their back up players a runaround. Still even Belgium/England 'B/C' will be formidable opponents. England will likely be all EPL players whoever they play.
Maybe there is just a lack of available Euro sides, who don't already have all their game slots filled over the Oct-Nov windows. Mexico and the US (like NZ limited to Euro based players), AWs on face of it should be more competitive against.
These games IF they happen are all about building towards the June 2022 intercontinental playoffs. That date will come around quick. Esp when all the AWs games in 2021 are likely to be OFC qualifiers. There is no Confeds Cup next year. So if NZ progresses out OFC, suddenly you come to start of 2022, with only the March 2022 window before you are into those 2 huge games in June 2022.
You also have younger players like Bell, Singh, Just, McCowatt, Cacace coming into the top XI now, who are still virtual strangers to older heads like Smith, Wood and Thomas. These guys all badly need to play games together against quality opposition. It's just a pity looks unlikely some of those MLS CBs (Boxall, Reid, Tuiloma) can travel to the EU.
In the big picture no one's going too really care too much about a 5-1 drubbing from the Three Lions, if it helps in some way prepare the AWs to beat Iran over 2 legs and get to Qatar.