This is an interesting take on the ideal size of a smartphone being 6.1”, I have to push back. Having owned quite a few different models of iPhone (from the Mini to the Max) and also dabbled with Android I’m here to say that there is no ideal. Everyone is different and you won’t please everyone.
I’ve settled on the iPhone 13 Mini and I love it, but that’s me. I have RSI and this phone allows me to give it a bit of rest and recover. Others love the Max and sacrifice comfort for screen size or camera.
Bigger phones are popular mostly because they are a computer replacement for a lot of people. As we do more and more on these devices a lot people want the biggest screen they can afford but there will always be those that just want something manageable (to them).
Unfortunately for those of us that like our smaller devices we seem to be the opposite of where the market is. I do hope that manufacturers ignore articles like this and don’t settle on 6.1”.