When I bought the Nexus 6 I gave my Nexus 5 to my son who, like you, recently complained that the phone was really unresponsive and had poor screen display issues. Mind you the phone is now getting on in life (having had two lives with me and him) and he is keen to get my Nexus 6 when I go with a new Google Pixel phone.
We know Alphabet/Google has announced an 4 Oct Save the Date when they are expected to launch up to 9 hardware products, including two Pixel smartphones. The two smartphones will have Google Pixel branding (not HTC) which implies that Google will have taken over total control of both the hardware and software and hence should make for a great, polished Android reference device to be known as Pixel and Pixel XL ("made by Google"). I really hope this smartphone is seen as every bit as good as say a Samsung flagship device so that we Nexus fans can finally say that there are no compromises with this one.
Why am I optimistic about the Pixel quality? Because with 7 other hardware launches rumoured on 4 October and the phones being the centre of the Google hardware universe (the other devices will work off the phones), 9 to 5 Google believes that Google has a lot riding on them. They believe we will have a Google hardware universe soon of tablets, laptops, smart watches, streaming devices, virtual assistants in the form of home speakers, a VR headset, etc and hopefully in a few short years a Google self driving car!
As we get closer to this complete hardware and software universe, a tight integration between hardware and software and overall reliability becomes key.
I am saving up for the Pixels as the entry point to this new Google hardware universe. Bring it on.