Welcome Alex! Good to see you here. I think you'll do well!
It's definitely still worth posting on both platforms.
Dan Larimer and Ned Scott started the Steem blockchain as well as Steemit.com.
D.Tube was created by @heimindanger
The videos are stored on IPFS ( https://ipfs.io/ )
Checkout this interview with @ned and @heimindanger discussing the future of Steemit and D.Tube recorded a couple days ago:
Videos exploring the differences between the entrenched centralized platforms an the emerging decentralized versions are interesting and highly relevant. Keep it up!