Is MPLS ever deployed in any Telecom Service Provider's IP network?

[learner of routing]

I'm writing a graduate thesis on QoS routing and just curious if MPLS
is really deployed by Service Providers' backbone network routers. Or
it doesn't have much usage besides implementing VPN?

What's the hot topic on routing technologies nowadays? I get a feel
that QoS routing is kind of a old topic once hot 5 years ago.

If anyone from the industry or the academic could provide any insights
on this issue, I'll really appreciate!

Jack Bates