I know what you mean about cat whiskers, and not crowding them to the edges of a frame...often a challenge in a "tall" shot of a cat from close-range. As to aspect ratios...I dunno....there are multiple aspect ratios in digital cameras. I LIKE the pro-Nikon in-camera capture option of 5:4 (aka 8x10); the 4/3 cameras are 4:3; the standard 3:2 ratio of most d-slrs is IMHO, NOT the best one for many portraits.
Personally, I like to crop to whatever looks best to me, and since 2013 I think I've _substantially_ cropped more images in post than I had in the previous 30 years. There's plenty of room for non-cropped images, or fixed-aspect shooting, or a mix. Then there's the old 1:1 or square. Every picture is different. I was taught NOT to crop, to show "the whole frame"...but that's a 1960's era affectation.