To put the Boeing/QR relationship in perspective, QR today is the 3rd largest operator of the 777 (2nd if you don't count the parked UA jets), they have taken deliveries of 83 777 from Boeing between November 2007 to June 2021 and have 3 second hand examples on lease. They had multiple 777 top up orders last one being in 2019 and have taken delivery of every single 77W, 77L and 77F they ordered. QR are also of the 777X launch customers with 60 on order making them have the second largest 777 backlog with Boeing.
QR is the 3rd largest cargo airline, right after UPS and FedEx in terms of scheduled CTK and scheduled tonnes carried (source: https://www.iata.org/contentassets/a686 ... diakit.pdf
) and the second largest operator of the 777F after FedEx.
QR was one of the launch customers of the 787, IIRC was the 5th airline to take delivery. Even after the battery issues and the groundings they went on to place a top-up order for 30 787-9 in 2016. They accepted deliveries of the first 7 787-9 without seats because of the BFE supplier issue, they didn't blame Boeing or find fault with the jets to not take them, they paid, took delivery and put the jets into service many months later after sourcing the seats.
So its not like QR is not a known quantity for Boeing for both established programs and as a launch customer, and QR continued to place and Boeing continued to accept orders from QR after the periods where the relationship was strained (e.g. 787 groundings).
With regards to QR being a launch customer, yes there were issues at various periods between QR and Airbus with the A350 but QR was the first airline to take delivery of both the A359 and A35K and have taken delivery of 53 A350s so far.