Yes, this looks like bitterness over your long stays in Vegas in 2019 which overall produced relatively little play.
Here is what I would do:
1) Call Caesars directly, and ask either for the host on duty or casino services. Tell them you want to take your annual retreat to Caesars. Don't tell them about being previously denied, just that you'd like to change Flamingo to Caesars.
2) If #1 fails, call your dominant property and ask for the supervisor of all the hosts. Tell them you want an AC-based host because most of your play is in AC. I have a feeling your Vegas-based host is acting in the interests of the Vegas market, and you don't want that as an AC player. Also explain to them honestly what's going on -- that you were led to believe that online slots were just like playing slots in the casino, and you put in heavy action. Make sure they know you were shocked by the inability to get a standard room at Caesars for your retreat, and you feel lied to, and are considering moving your action elsewhere. Be polite but firm about it. See if they can help you.
BTW I looked up the terms and conditions for this, and it did have two terms which work against you:
"Some restrictions may apply for transportation and hotel accommodations. Please reach out to your Casino Executive for details."
"Blackout dates apply and may vary by property."
So they can hide behind this, but you still have some leverage because you put in so much action online, plus you are a slots player, which they love to see. They're treating you like a video poker player who grinds the very best machines to barely achieve Seven Stars, and then sucks the benefits for 2 years. That's not you at all, even if you didn't play much in the summer 2019 stays.