Oddly, reminds me of when Apple first pushed/forced HEIC on all of it's users, without letting them know of course. Because of that, it caused thousands of students to fail their AP exams.
Big problem with HEIC is it requires H265 licensing because it's effectively a single frame of video. This is why Windows won't open HEIC by default is Microsoft didn't want to pay for the licensing
My Samsung was recording videos in Hevc by default the other day and it was a pain to edit them in Da Vinci Resolve. Luckily Kdenlive handled them without any problems
What compression settings are you using for each? If you're just accepting defaults it's quite possible you're comparing against a lossless webp, which is quite likely to be larger than jpeg at typical quality settings.
I just did a test with the test with the first png I found and tt looks like the default were lossless, hence why compression ratio were bad.
Here the webp in smaller than the jpeg and noticeably better. Maybe it would be different for different kinds of picture, with colours, more details and stuff, but here it is clear.
Some sites still don't support PNG lol. Usually it's places where they specifically expect a photo, where they'll hard code the validation to only check if it's a JPEG. I once had to upload a picture of my face for something and the original JPEG was too large, so I took a screenshot and tried uploading that but it wouldn't work because it only accepted JPEGs. So I had to figure out how to compress the image locally on my phone because I didn't want to upload a picture of me to one of those online converters.