Living in Russia, I had some idea who Durov is from his interviews and reputation and actions, before Telegram when he was in control of VKontakte too, so I never was a Telegram advocate.

Also that mtproto is a load of hacky crap is something people were writing whole articles about from the very beginning, and their arguments that their IM is "secure" were also quite typical for frauds.

But, still, at some point it was usable. EDIT: And there was hope for alternative clients pleasant to use.