Image size restriction vs third party

If I use cs-cart image upload size restriction to limit image size to 5MB and use third party compression like AB WebP images to reduce image size to 10%, would I effectively have the same page load speed as if I used the cs-cart image size retriction to 500KB?

I don’t care about server space and it is just page rendering speed to user that I am concerned about.

Trying to balance user experience (vendor doesn’t have to compress images) vs server surprise (so sure, I care a little bit about server space).

You could likely optimize images much greater than 10% and get amazing load time.
That’s the case for our site and we deal with thousands of optimized webp images.

“You could likely optimize images much greater than 10% and get amazing load time.
That’s the case for our site and we deal with thousands of optimized webp images”

Reducing by to 10% of original size is approx 90% reduction. But the question was how does performance compare if I (for example) limit image size to 5MB and then using a add-on to reduce the image size to 10% of original size (i.e. a max of 500KB was compressed) vs limiting max size of images to 500KB upload size.

The later being more incovenient to vendors, meaning I would prefer the first option but not at the price of a big performance hit.