Nope.

If you're managing a 100+ user channel, encryption matters fuck-all unless your invitation process is 100% airtight and every user has all their devices encrypted and locked up at all times.

Data will leak anyway so E2EE won't bring any real advantages.

That was a rhetorical question, of course, but thank you for confirming my opinion.

Political parties typically do, and some are known to use Telegram for their internal groups.

Any leakage of secret knowledge shared only through these groups could be detected as treason by one of the participants in that channel. Having several channels with fewer and fewer members, closer to the party's leadership, is a typical configuration to maintain control of the most secret information.