I will honestly say that I have no idea how Deezer works on individual platforms. I've never used it before. I will say that while stand alone devices, like Roku or AppleTV, are typically a good deal better than what is built into TVs, receivers, or Blu-ray Disc players. But, that doesn't mean that the app they are using is good. The 10 foot interface that is used in most products is developed by the product manufacturer. That means that Deezer is responsible for creating the interface that most manufacturers will use, and the fact that it is slow, choppy, weak, is a Deezer issue more than anything else. It was not up to Roku to keep Deezer on the platform, it was up to Deezer to ensure Roku had a working interface. Reach out to Deezer and let them know you used it regularly and aren't happy it is gone. Explain how bad the interface is on the other products you've tried.
While I haven't used Deezer, I'm a big fan of there being options and I think they need to put their best foot forward across multiple platforms. Deezer may be focused on ensuring their iOS and Android interface is the strongest it can be, which may not leave them the resources to develop a good and proper interface for other platforms or a really solid 10 foot interface.