E2EE is optional on Telegram and not really convenient. You can create a private chat which will be E2E encrypted but this takes a few taps and pins to device. Most of the users don't bother. And the main target is not personal chats but channels which can be easily discovered and followed.

This is not an e2e battle, this is the hunt for channel owners. Frankly it is too easy to make a "local chat" and sell stuff. Durov has the data and this is his weakness and strength. Platform is viral but there are too much for one hands.