Not going to buy another new Asus router after having been able to use my 87U as a router for only 3 years
The RT-AC87U still works, and still gets security updates. If you think the grass is greener elsewhere, you'll be disappointed. Asus are among the manufacturers who provide the longest support for their routers.
Netgear's own Quantenna router (the R7500) was dropped after about 18 months. Meanwhile, the RT-AC87U with almost identical hardware and released almost at the same time still gets updates despite being almost 6 years old (not 3 like you mention).
Amazon was selling it new only last year and Asus own firmware was already basically dead.
The last RT-AC87U firmware update was only two months ago, so not sure what you are basing this on.