Never said anything about how you mentioned TweenService doesn’t work. TweenService can do everything these methods can and more. Typically it’s in your best interest, especially if you want to modify multiple properties in one tween, to use this.
There are many methods that shouldn’t be used yet they exist. The existence of a method doesn’t imply that it should be used. Furthermore, method usage is case dependent.
TweenService and the isolated GuiObject tweens look the same but internally they aren’t. TweenService has much more capability and support over these methods which by now are considered legacy and could be deprecated in the foreseeable future. They may be kept for compatibility purposes.
I don’t really know why you’d want to wait for an official post before taking a recommendation, but that’s on you I guess. Members out here are just looking to help users.
As for the blog, what post are you reading from? The blog doesn’t necessarily have updated information and TweenService did not exist at the time of those two methods. The Developer Forum and Hub contain the most updated information about development practices. The blog is primarily for Roblox news, not development updates. This separation is already very clear.