It’s understandable to feel that way, particularly since a lot of the formal breathing exercises we know in the west come from yoga practices which are thousands of years old and have all sorts of metaphysics tied up in them. But it doesn’t seem too hard to believe that having a nasal cavity to regulate air temperature, block dust, increase moisture, etc would be beneficial to the lungs.
Here is one somewhat extreme experiment on rats that showed continual mouth breathing had negative cognitive effects [1]. There is also research that has correlated nasal cycle dominance to different cognitive functions [2]. I’m not totally sure about the covid-19 links this paper makes, but it’s interesting to note the sinuses help create nitric oxide and NO plays a wide range of biological roles [3].
Personally, I do pranayama every morning before seated meditation as well as right before bed and find it to have great emotional benefits if nothing else.
[1] https://www.jstage.jst.go.jp/article/josnusd/61/1/61_18-0006...