I wouldn't say it is unfounded. Balance in 1v1 for the competitive scene had precedence in the first patches iirc. It doesn't mean that every change to 1v1 were bad or even affected 4v4 in the first place, but if those two modes were colliding then 1v1 was usually considered more important.
Imo the problem lies elsewhere and it is not 1vs1 mode VS 4vs4 mode.
The MOD team has made an attempt to increase the diversity of unit being used which is a good thing. The problem generated from the fact some times even when a unit is slightly OP the effect can be amplified in large modes. (some times the same work the other way round).
Imo one has to keep in mind that not all units/abilities/commander can be equally useful across all modes. The game simply can be played in similar manner in 1vs1 to 4vs4.
It is accurate that there was a time that the effort to balance the game was more focused in 1vs1 and larger modes where neglected. That seem not be the case any more.
But imo that does not prove a correlation where when ones fixes 1vs1 balance one ruins 4vs4 balance and vice versa as OP seem to claim.
In sort I think we basically agree.