Took a peek into this - was hoping to see a ray of sunshine for you. Unfortunately, Google's relevant
Pixel 2 XL Warranty declaration seems unambiguous:
Google warrants that a new Phone and its included accessories will be free from defects in materials and workmanship under normal use in accordance with Google’s published user documentation for one year from the date of original retail purchase in its original packaging by you.
The inclusion of "by you" narrows their obligation so that only the original purchaser has the right to demand warranty service (unless, as later stipulated, your State has specific consumer laws that afford exception). They did, as you noted, later officially extend the warranty term on the 2 and 2 XL, but that only extended the duration of the warranty term, with no modification to other terms such as how or for whom warranty coverage is provided.
As to what numerous reps may have said to you...
No employee or representative of Google or its affiliates or any third party is authorized to make any modification, extension or addition to this Limited Warranty.
...Google's representatives' statements, correct or incorrect, cannot be used to hold Google accountable to providing any services outside of those outlined in the governing warranty, regardless of how they may have occasionally elected to handle similar instances in the past. In your shoes, I'd try to seek an empathetic exception from a supervisor, noting that the spirit of the warranty as expressed to you by the employees should be followed, even if the letter of it doesn't mandate it - but it sounds like you've had no luck going that route.
While no longer an issue for you, in regards to the 'blacklisting,' Good to hear it was removed, but, if my distant recollection of how that worked some 10+ years ago was an remains true, Google wouldn't have been the only one able to blacklist your IMEI - any wireless provider that had previously provided service associated with that IMEI wherein that associated account had defaulted on payment may have been able to take such an action.
Very unfortunate circumstance, as the camera is one of the greatest aspects of the phone. If you're willing to forego assured warranty coverage with secondhand phones in the future, you might want to try Swappa, which is less filled with vermin sellers.