"increasingly less so" is a correct and usable phrase in written English.
It is typically used to describe a gradual decrease in something. You can use it anytime you want to emphasize that something is becoming less and less true or noticeable. Example: As I grow older, my energy levels are increasingly less so.
Full-time residents buy there, but increasingly less so.
You often used to get away with it, these days increasingly less so".
Navalny argues that he is not necessarily more popular himself, only that others – notably Putin – are increasingly less so.
A Lebanese Christian man who has lived in Qatar said that while his home country was liberal about drink, dancing and parties, the Qataris were increasingly less so.
But state records show that Mr. Bush's appointments still tend to be overwhelmingly white and mostly male in a state that is increasingly less so.
(Jon Pareles) TIM FITE (Friday) Mr. Fite, from Brooklyn, dabbles in classic acoustic folk and hip-hop — still an unlikely pairing, although increasingly less so — and his scrappy, defiantly lo-fi songs are difficult to classify.
Another important difference between the new archetype of futurism and the one envisaged in the 1960s will be that objects will become increasingly distinctive, rather than less so.
Reanalyzing the medieval Black Death and verifying its etiologic agent is becoming increasingly important, and not less so, in an age of rapid environmental and population changes.
Wind reports from ships at sea have become increasingly based on anemometers, and less so on the Beaufort Scale.
At the country level, and less so but increasingly at the regional level, UNICEF has acted in a timely and proactive fashion to lead or facilitate interagency processes.
Payers are tightening control over drug spending and are finding physicians and physician groups increasingly less reluctant allies in doing so.
