They're old models that don't support the latest technology.
Only GT-AXE16000 is the best.
No, they are not (all) old models.
I would agree that the GT-AXE16000 has the best paper specs today, but that doesn't mean much (and therefore can't recommend it) when I haven't tested one myself. And even the paper specs won't mean much when WiFi 7 equipment will launch soon enough as-is. Then even this model will be outdated at their availability dates.
The best new router is the GT-AX6000 because it offers the best balance of hardware and features today. In addition to noticeably improved performance (~20% faster throughput than the last 'king' I've used extensively; the RT-AX86U).
The GT-AXE16000 will be equivalent to all the previous router's first tries at the newest standards (i.e. good enough for today, but not worth buying when a Gen 2 or Gen 3 model is released soon afterward).
As an example of that, the RT-AC68U was great when it debuted, but was eventually outclassed and outperformed by the RT-AC3100, and later, that model too was shown as outdated when the RT-AC86U appeared on the scene - for AC class routers (and specifically for 1Gbps ISP speeds). Even if the RT-AC3100 still holds the range coverage record in my environment, it doesn't justify its price and can't hold a candle to the networking performance of the RT-AC86U (and for the record, I never saw/used a faulty one as reported on the forums here). And all these are surpassed by a 'lowly' RT-AX68U.
And with the above of the way, the best router is the one highest level and with the most balanced hardware, at the cheapest price, which gives the most performance and is widely available today. That title goes to the GT-AX6000 hands down. Any other Asus router today is a trade-off, from what I have tested in my own environment and/or in my customer's environments too.
If you are using it as the main router
and you want to use it for as long as possible too.