Yes that is what I said. Once you sign in either via the gamertag or your Microsoft account it signs you into the game automatically after that.
Or you can use one of the many different versions of Solitaire available free from the Store that are not Xbox apps.
Regarding the first point, what of folks who either refuse to use a Microsoft account or don't want to create Yet Another Account regardless of how few times successfully doing so removes the constant nagging and pressure to do so? It is very much akin to paying the danegeld.
Their only options are to cave in and do what they shouldn't be compelled to do (what they should only do on a deliberate and well-informed decision without persistent interstitial nagging), to endure the trouble of finding and installing a suitable competing product regardless of the relief-bringing reward doing so offers, or to endure the trouble of removing that which should never have been installed in the first place.
Regarding the second point, while I agree completely that installing just about any other solitaire app is the best workaround, it overlooks the fact that this is an out-of-box experience problem with this new operating system. This is the heart of every complaint to Microsoft about Solitaire in Windows 10 that I have seen and which I share.