I’m not sure how important it is. My first phones with replaceable batteries sucked, the plastic cover would always pop out and was generally a point of failure. And it never did me any good, as most phones died before the battery became an issue.
Today I’ve had an iPhone for 3 years and the battery is still going strong. If I need to replace it… I’ll just find someone who can replace it, easy enough. Sure it would be more convenient to be able to do it myself, but if it happens once every 4-5 years I honestly don’t care, and will take the daily convenience of no plastic cover instead.