I have Affinity Designer. I like it. But Xara is the “all in one” tool. Certainly Affinity has some great newsletter capabilities, and offers some very handy presets especially for Facebook and Instagram. Affinity is a great mock up tool. Works well on Mac too.
Xara’s power lies in adjusting on the fly. For web very handy for photo enhancement again on the fly. It all depends upon your workflow and tools.
If one has another web product, Adobe, coffee cup etc, Affinity is a tool to add to the toolbox.
Affinity at the moment is not interested in producing a web program. Certainly Affinity Photo is an excellent replace for Photoshop.