TL;DR To be fair to Telus, this is probably more to do with how HBO colour graded the final video that Pik, Crave etc stream, and how some TVs handle blacks (not well).
However, the lower bitrates used by services like Pik and Crave make it worse, so that is a Pik related feature request I'd make — options to choose the level of streaming quality, like Netflix allows. But that's not a trivial feature to implement.
GoT was certainly an exaggerated example I'm not buying that it isn't a pikTV problem. I spot checked a few more offerings that are both on Netflix and PikTV and PikTV globally has a contrast and quality problem that is quite noticeable.