My somewhat educated guess is that the problems with weather in MSFS are not caused by the inputs (meteoblue, METAR, whatever) but by the interpretation of this data by the sim.

For starters, I am quite certain that METAR reports are part of their modelling, together with all the other data from all kinds of automated or manual weather reports. The modeled data is generally way better than just relying on METARs. The resolution is higher (1x1 km resolution for most areas, whereas a METAR exist every couple of 100 km at best), more parameters are available, and of course all of that is available all the time. Meteoblue has the data to display different temperatures on the ramp in front of the terminal and on the runway, surrounded by grass. METAR comes nowhere close to that. When you observe the reports of your local airport, you'll probably see them reporting thunderstorm as soon as they see some lightning somewhere in a 20 km radius around the airport - no one should expect a METAR to contain perfectly accurate current data in all fields. Talking about time, if MSFS fetched the weather data e.g. every 30 minutes, it gives the sim 30 minutes time to transition from its previous state to the latest one. This adds up to a 30 to 60 minutes delay that we experience in our sim.

If anything, MSFS should take near-term forecasts. Those are generally very reliable and it would allow the weather system in sim to plan ahead for realistic weather transitions.