I do not think you can use that directly to evaluate the success of any ICO because when you look closely you will understand the reason why many ICO have a high member on telegram group, is because of two things. firstly, maybe the ico has bounty which makes it compulsory for participants to join their telegram page of the ICO. secondly, maybe a certain percentage of the bounty is allocated to telegram page so many of the bounty participant will like to participate by joining the telegram page of the ICO
This is very alarming now, the number of members in telegram group of some ICO are not all investors,
More than 50% of them are just there because of the Airdrop requirements.
Some of those too are bounty hunters, they are just requiring participants to join the ICO group.
Because investors seeing telegram group is the big impact of ICO success.