That the above features do often occur in most mammal species is undeniable. But that is not the point. The point is that an animal such as the platypus is considered a mammal because it has mammary glands even though it lacks many of the above features.
The larger point as I have mentioned several times, and you evolutionists totally ignore, is that extrapolation just confirms prejudices, it adds no new knowledge. For example, using the platypus as an example again. If it was not a living species, it never would have been classified as a mammal, none of its uniqueness such as its killing poison, it's sensory radar, it's egg laying, its not having separate excretory and sexual ducts and many other interesting features would have never been known. It would have been just one more set of bones like any other stuffed into some procrustean bed by lazy paleontologists.
No. The platypus is considered a mammal because it shares these features in addition to having mammary glands. If there were no know extant platypi (sorry, Plato) their fossilized remains would still be classed as mammalian because of these other features.