Hmm, as a Scot myself I wouldn’t necessarily agree with that interpretation, still less the paradigm or theory that support for Unionism can be correlated with relative lack of proficiency in, or widespread use of, Gaelic.
One of the main hubs of support for Scottish Independence was cosmopolitan, lowland Glasgow - Scotland’s largest city, which does not have a Gaelic cultural heritage (as in regions of the highlands) but rather has spoken English - mingled with bits here and there of “Scots” that has become, somewhat wrongly, known as slang Glasgow
patter - for centuries.
By contrast, the Highland regions where Gaelic and traditional tongues are widely spoken, voted very strongly for the Union.
Dundee, North Lanarkshire and West Dunbartonshire were the other regions that voted for independence - all in the lowlands, none Gaelic speaking.
The highest percentages of Gaelic speakers were in the
Outer Hebrides which voted about 67% to remain in the UK.
It thus cannot be used as a good indicator.