I've not seen any indication of that. I think people are comparing everything to the AC68U which was fully supported for more than 10 years. I don't think any other router in the ASUS stable has seen half that. As has been said many times by others, most other manufacturers (Netgear being an obvious example) are unlikely to provide more than 2 years of updates that are spaced 4-6 months apart.
And when picking an ASUS router, its important to consider whether its a fringe model, new product line model, or something more main stream. I consider the AC86U a fairly main stream model (as evidenced by the large number of people that have it), and it got 5.5 years of full support. If it weren't for AX, it would probably still be fully supported because its a fine performing router. I have an AX6000 that I'm testing, and in the casual tests I've performed thus far, there is no improvement in wifi range.