Okay, let's say certain ONT on certain ISP, and some routers, may have issues with bufferbloat score of "C" or "D", is there a real problem in reality?
Take example of SingTel new ZTE ONT, the upload gets bufferbloat issues. Is there a real impact? In most use cases, download data are much more than the upload. And take note upload speed is still good in the tests.
From what I read, QoS and SQM are usually doing more damages to symmetrical 1Gbps and above Fibre internet services, as typical home routers can not handle QoS/SQM properly at 1Gbps, including Ubiquiti/MikroTik.
Yes, bufferbloat was a thing in the days of dialup.. You'd have a (typically) 64kb transmit buffer for a 33.6kbps (max) modem, so it would take nearly 20 seconds to empty the contents of the buffer. It was designed this way to improve throughput, because operating systems of the time (especially windows) could not respond quickly enough to send more data once the modem was ready to transmit it.
It happened on things like ADSL too, as many providers would give you an extremely weak uplink it may still take a couple of seconds to clear the buffers.
For a 1gbps connection, the buffers are tiny relative to the speed of the line - they should get cleared very quickly. Similarly, your internal devices probably aren't capable of throwing data at the router faster than the upstream line can accept it.
What's more likely a cause of latency, is the router itself not being able to handle the traffic rate. Adding extra complexity like QoS, NAT, firewall rules etc will exacerbate the situation and slow it down further. Remember these devices are built to a price point, with corners cut to make the price more attractive. You'll get better performance with a high end layer 3 switch, but most home users won't pay the price or tolerate the fan noise.
me getting obsessive 
