This is a complete non-issue. I have no idea why people are complaining about this, except as another way in which Android users are trying to force their ecosystem choices on everyone else. The majority of people globally don't even use built-in messengers, they use WhatsApp or a similar application, most of which uses similar stylistic design choices as Apple uses for SMS, so it's hardly an issue.
I'm well aware that high schoolers get bullied for being poor and not being able to afford an iPhone. High schoolers were getting bullied for being poor and not being able to afford fancy clothes before cell phones were even a thing, and prior to smartphones were bullied for being poor and not being able to afford pagers or a cell phone (or a car, or ... or ...).
High schoolers are assholes and will find some excuse to torment each other regardless of what aesthetic and design choices somebody in Apple's UX team makes for their built-in messaging app. This is a massive nothingburger and I honestly have no idea why the media gives this any credence other than the shift of the media generally towards being anti-tech.