I've been using fondleslabs for a long time, and based on early experience:

• Nexus One - 3.7" display, too small to be practical
• Galaxy Nexus - 4.6" display, better but still small
• Nexus 7 - 7" display, sweet spot ✅
• Samsung Galaxy Tab 10.1 - 10.1" display, cool tablet, too huge to hold

I used to spend more time with the Nexus 7 than any other device.

Nowadays, a Galaxy A35 has a 6.6" display, which is pretty close to the "sweet spot". While I can't comfortably hold it with one hand by itself, a Magsafe case and a PopSocket, let me hold it in multiple ways (a Qi charging addon under the case, allows wireless charging while protecting the USB port, without spending four times as much on an S series).

I'm not surprised at all that flagships are converging towards 7" displays. Smaller phones are for special use cases, like some ruggedized models.