@HYPER_PnMMS file size limit depends on the carrier, but usually is set around 500 kB, while photos taken by smartphone camera occupy several MB. there's no need to avoid compression if you want to send your photos that way.
that said, Android Messages (the default SMS on your phone, made by Google) is pretty horrible at compressing images, I agree with that. there's no way to fix it in the app, but you might want to try some apps from Play Store. Textra SMS or Pulse SMS, for example, compress photos in a way that doesn't affect the quality as much as Android Messages. you also might want to send feedback to Google by finding Android Messages entry in Play Store, scrolling to the very bottom of the page, and tapping "send email".
