Blocking ads is the only reason that makes me depend on root. I built a script[1] that generates flashable zip and from time to time I update it on my phone.

[1] https://github.com/zant95/hBlock

The primary motivation for rooting the phone in order to be able to modify the hosts file was to block ads in ad-supported free apps. Another low-tech method for achieving this was to put the phone into airplane mode while using the apps.

When it comes to the browser itself, another common method for adblocking was for the adblocker to function as a proxy server that you'd setup in chrome, and you didn't need root for this.

Also, you can just use Firefox for android, which lets you install same extensions as on the PC version, including adblockers.

This is where MITM can be very useful. You can still configure the DNS server to one you control, and which blocks the domains you don't want. I believe you can still install your own certificates and MITM the rest of the traffic too, filtering it through a proxy like Privoxy or Proxomitron. The availability of VPN means you don't need to be at home to have a filtered connection, but you do need another machine running the endpoint+proxy.

That's why you should be using Firefox.