I haven't seen any Gamblig Platform who used Telegram for Promotions, most I know is that they use Discord.
Do you have any Idea why they don't have any Telegram Communities? and why does it seem they don't use this platform for their promotions?
Feature wise Discord has a lot to offer than Telegram, the admin of the channel can create a sub topic or category and he has full control and can restrict spammers, it started as a video gaming but now they are revising it to become an all purpose communication they have a new slogan "A place to talk" and revised their website, it's better than Telegram on many features.