Yeah blame router when port forward doesn't work due to cgnat 👍

Nothing much. Just not possible to saturate bandwidth in single tcp connection (which is unrealistic in real-world usage anyway due to typical prod server limits).
Also added points of failure.

Well its up to individuals.
Have you heard the popular saying about mentality about food and eating out?
Something that goes like, poor people will only care about quantity, middle class care about taste, but wealthy people care about experience.

The same with internet, not everyone sticks with poor people mentality. You not necessary have to force yourself eating every single grain of MBps you paid with your hard earned money. Or stuck with bare minimim package that you that you think you could utilize 90% f the time.
Most people out there could afford and willing to pay for tasty and enjoyable internet (reasonable speed in any usage scenario), or experience (downloading 10gb files in less than a minute in a rare moment that happen only once in a while).

Its not a wrong decision if you could afford and you have a reason for it.

So apa citer ni kawan? 10 days left.

Whatever happened past the lan port side of your onu is none of TM business. They probably feel better if you use your own stuff knowing fully well their stock router is shit.