I've been non-stop troubleshooting and playing around with antenna positions and AP settings trying to get the 2.4GHz and 5GHz to kick out as much throughput as possible.
On 2.4GHz, the BT Smart Hub can output 105Mbps
On 2.4GHz, the Linksys router can output 85Mbps
On 5GHz, the BT Smart Hub can output 250Mbps
On 5GHz, the Linksys router can output 180Mbps
Both routers have the same channels and channel widths. The link speed from my LG V30 on 2.4GHz for both BT and Linksys is 144Mbps, and 866Mbps for 5GHz respectively.
I know that Linksys has been bought by Belkin and the Marvell division has been sold off but surely a ISP router/AP can't perform better than a high-end router? The BT Smart Hub doesn't even have detachable antennas...
Don't overestimate the value of detachable antennas, with good antenna- and rf design, even PCB antennas in (especially-) the BT Home Hub 5 Type A can do pretty amazing things.
The differences here are mostly down to the wireless chipsets, QCA-Atheros and Marvell (soon to be NXP) on the other hand, there can be differences in various ways (not the least interoperability, something mwlwifi seems to have quite some problems with, e.g. esp8266 in particular). Other QCA chipsets would
probably achieve even higher throughputs, as the AR9227/ QCA9880-BR4A WLAN is slightly hampered by the I/O performance of the lantiq SOC (which is limited in terms of I/O performance, relative to ath79 or ipq40xx/ ipq806x).
Just as an unrelated sidenote, Belkin, which owns Linksys, meanwhile got bought by the Foxconn Technology Group/ Hon Hai Precision Industry Co., Ltd.
fwiw, did you test the WRT1900ACS with OpenWrt and stock LInksys firmware?
Yes. I tried the stock firmware and there was no difference in terms of performance.
P.S I thought I posted a reply months ago. I'm sorry if I'm replying back so late.