I think this is the key part: thinking about my friends and family, over the last few years everyone has switched to using the box which came from their ISP except for a few IT people and gamers.

This is generally a good thing since the ISPs are significantly more likely to install security updates, and WiFi speeds exceeded the average home internet connection somewhere around a decade ago so the benefits to buying your own are fairly limited for most people.

Depends where you live. There are ISPs that will get you 250 Mbit downstream via FTTH, but their WiFi supports only 802.11n over 2.4 GHz only. When your neighbors get similar setup, you will not get over WiFi anything that approaches your Internet speed.

People think they need repeaters, cable installation, all kind of expensive and worrying projects... nope, just use a real wireless router instead of the Comcast box.

Yes they do, but they shouldn't.

The problem is that you place your all-in-one cable-modem-router-AP at the point where the cable enters your house. This is unlikely to be the ideal position to place an access point.

For example, my fiber connection enters my home at one of the corners of the house. You want your AP in a central location.

Are you thinking of other issues besides signal strength?

Apple is nudging consumer behaviour with each product transition - I wouldn't be entirely surprised if we start seeing more devices with mobile data built in (say, with an antenna behind the logo or behind the Touch Bar).

I'm a network engineer and use pretty much "enterprise" gear across the board at home. A couple of years ago, though, I yanked out my Cisco ASA firewall (connecting my home network to my ISP) and replaced it. I'm now using a (expensive) "RouterMaxx 1106" [0] (PDF) as my home router. It was designed for and shipped with Mikrotik RouterOS but I replaced that with pfSense, initially, and then switched, later, to OpenBSD. It Just Works(TM).

The hardware, for the most part, doesn't matter too much. The software you choose is much more important, in my opinion. Choose something that can be tuned and locked down as needed and, critically, gets updated regularly. I'm a "CLI guy" and quite comfortable with OpenBSD and a terminal so this setup works for me. For those desiring a point-and-click web-based method of administration, pfSense, OpenWRT, and similar may better serve their needs.

n.b.: FWIW, my router doesn't provide Wi-Fi, only (6 x 1000 Mbit) wired Ethernet. I have been using an Aerohive AP330 access point but am currently replacing it with a Ubiquiti Unifi AP AC PRO.

[0]: http://www.balticnetworks.com/docs/routermaxx%206%20port.pdf (PDF)