Yeah, exactly a stress test. They will want to see how popular the Urgent Quests can be & if they would put extra strain on the server. Hence offering an incentive to partake. Which is exactly what a beta is for, to test all possibilities. So how you think that detracts it from being a beta is beyond me.
I don't think calling free cosmetic rewards, in a free game that we got to play early "inappropriate" is reasonable. The length of the beta was outlined plenty of time in advance & there were tiers of rewards depending on how many UGs you made it to, as well as rewards for simply logging in.
They even adjusted the Urgent Quest schedule & gave us extra time for the Closed Beta to make up for the initial server down time. They didn't have to do any of that in a closed beta. It was very, very reasonable.