Great that your are taking things with humor...
The point is low-latency traffic shaping is quite CPU demanding (not so much throughput, but low-delay), and the actual load depends on packet size, and the available CPU cycles depend on how much other work a router needs to do. Traffic shaping @1Gbps is quite a lot of work even with maximum sized packets (1538 for ethernet):
1000*1000^2/((1500+38)*8) = 81274.4 pps
or
1000/(1000*1000^2/((1500+38)*8)) = 0.012304 milliseconds per packet...
IMHO traffic shaping @~1Gbps is possible with a few consumer-grade non-x86 routers, but typically there are little reserves for the unexpected, so depending on what else a router does you will fail to achieve the ~1Gbps throughput.
For example my turris omnia, when streamlined to only do minimal other chores (like no wifi) and with all configuration tricks I managed to come up with (manually adjusted packet-Steering) allowed bidirectionally saturating traffic shaping at 550/550 Mbps (or unidirectional 1 Gbps), but adding a few more services degraded that shaping performance considerably (my access link is only running at 116/37 Mbps, so even with other duties traffic shaping with cake is no problem).
I guess the issue here is to come up with the correct expectations, since 1 Gbps ethernet interfaces have become ubiquitous and many cheap routers manage to do NAT/PPPoE/firewalling at 1 Gbps rates one intuitively assumes that network processing at 1Gbps to be a piece of cake. Once one realises that OEM firmware often only achieve throughput close to 1 Gbps by employing accelerators (which often are very specialized and only accelerate, say PPPoE, under very specific conditions and not generically, think unencrypted PPPoE running like a bat out of hell, while encrypted PPPoE (I do not know of any ISP actually using that, so this is a thought experiment) probably would be punted to the routers main CPU and hence achieve considerably less throughput) the main CPUs of those routers often are not up to the task of doing much at 1 Gbps.... Traffic shaping however typically is not something offered by those accelerators, so sqm/cake do not profit of thse and hence running cake/sqm will expose a router's raw CPU capabilities, which often are not as high as expected.
And for good reason, as far as I can tell it is the only/best-supported WiFi6 router under OpenWrt...
Well, we can have a look there if you want. I would need the output of:
ifstatus wancat /etc/config/sqmtc -s qdisctc -d qdisc
as well as the link to a result of a dslreports speedtest, configured like this (please note the dslreports speedtest is somewhat in decline, but it still offers a few unique pieces of information).