If they open up that just allow the use of other tools with the sims. It’s not a bad thing. If you do not use them you just don’t purchase them and use the weather provided by MSFS.
There is a lot more than just archived weather. It’s also a lot of work on smoeething the changes, good turbulences representation and so many tings that are not really visible. Even interpolating weather for places where you don’t have actual data sources.
What makes a great sim is for it to be completely opened to thrid parties so they can bring in more stuff that the sim developer can. For example no matter how good Asobo are they will never have a jet as close to the real thing as PMDG, FSLabs, Majestic, and so on. Simply put Asobo can’t spent years on a single aircraft model, while those compagny can and really pushes what our sims can do.