Yes and no.
Yes, because it was slowly developing and missed all the stuff that changed over the years. No, because there is a new version, not sure if it's out yet. It is or will be vastly improved but compared to Lutris, it still doesn't offer as much potential. It doesn't have dxvk, gamemode and other good stuff. Basically all you could do with playonlinux can be done in lutris and so much more. In certain situation POL can still be usable thou. However, a new translation layer is coming: the one translating DX9 to Vulkan and its development is going fast. Finally older games will not be so slow, so Mass Effect 1 or Skyrim will be given a new life: less bugs and highly improved performance. Now DX9 games, although old, can be laggy, while DX11 game like Witcher3 is outperforming them.
In such pace, dxvk and similar projects will be the core of the gaming, both in Proton and in Lutris and given the fact that POL offered only wine versions which mostly translate to OpenGL which is inefficient, obsolete and buggy, I don't see it being used anymore, unless they add those new X something to Vulkan translation layers.