In regards to this, there are still highly manipulative practices that occur, that's with groups in excess of 15-20k members.
Most naturally grown Telegram groups consist of 5-15k members, before a sale is finished or finalized. Anything ranging from 20-100k, that was made post-2018, is consisted of fake, accounts pulled from other groups and other highly manipulative practices. These types of crypto groups you should always avoid.
Concurrently, there are a lot of "influencer" groups consisting of a few thousand members, with a crazy amount of activity. These are also highly faked telegram groups, running bots with fake messages and or paid messages for a specific time, to make the group appear active in order to sell AMAs or other public events for crypto teams. If you're serious about crypto in any way, then you won't be in these groups listening to some guy talking about the latest coin he's shilling. It's great for quick research, but always know these guys are in it for themselves, they are ultimately looking to profit from your voice, time and activity; just like any tech company in the real world. "Data is king."
All in all, when in doubt, view groups like Binance's groups, Binance's shilled IEOs and see how many members they have. Chances are, it will denote a reasonable Telegram group community size for any given period in the broader crypto market.
Also, as OP said, never invest based on the groups. A lot of shills, a lot of FOMO, a lot of nonsense and a lot more shady motherfuckers; all there to solely manipulate your thoughts. Even worse are the groups who ban users for giving critical feedback (in a non-shit talk way), because it may cause other users to ask the same questions.
Most of those very large groups have bot members, very true sir. I was astonished to see an advert by someone saying he adds fake members at the rate of 1000 members for 5$. This means one can easily add 10k members with just 50$. Some bounties even have telegram activity, aside from the bot chats you mentioned here. Investors who get carried away by "large community" will always fall prey when they see these large telegram groups.