Yep. It is a partial solution. Another part is pinch or tap to zoom. Another part is landscape mode. Another part is the the accessibility settings.
Point is that there are already multiple ways to address the problem you described without making the screen bigger. Though I don't begrudge you the desire for a larger screen! Personally, I've only had rare problems reading websites on the iPhone. Mostly due to horrible web design.
Those aren't solutions. Pinch to zoom requires time to navigate a page versus being able to simply read all the text comfortably by default. Landscape mode almost always helps but still you need to flip your phone. Accessibilty has nothing to do with rendering text in Safari.
The truth is that a wider phone in portrait would be just as easy to navigate with your thumb. The issues start to arise when your screen is very long, like with these new 4.7" and 4.8" flagship phones. The 4" iPhone screen should not have this issue.