Who care about actual phones, what matters if the OS it runs, and Android is far larger in that sense.

Both metrics are equally useful or useless depending on what you want to quantify.

If you compare this to "serious" gaming technology (i.e. what the triple-A creators are making, and what parents are willing to pay $70 dollars a title for to keep their 16 year old from nagging them), the iPad and iPhone both are severely lacking in computational power to produce anything that the heavy consumer will spend "real money" on (rare exceptions like Farmville and Candy Crush not with standing). This is completely useless for serious gaming.

This could be huge for, say, realtors though. Being able to show your prospective purchaser who really likes the home but feels 'iffy' about that wall blocking off light into the dining room can now power up an app and show in real time a rendering of how the house would look if you knocked out that wall and had an open-floor layout with that beautiful Southern light pouring in. The ability to pop in new landscaping to let the buyer visualize what could happen if you replaced the front with hedges + hydrangeas against hyacinths could easily make the difference between that realtor making her 6% on that $850,000 or not.

A large portion of Android devices are very slow.

A large portion of Android games are not that demanding. If you saw what people spend their time on in the metro/train...

Can most of those Android devices run AR, or anything much at all?

Never seen anyone using AR in real life apart from some gimmicky stuff. The idea is nice, the execution is lacking, and the applications would be way better if you had it always on (as in, glasses or something similar), not through a phone or tablet surface.

GP is comparing phones, not operating systems.