We will first need to delineate a few things here. Outerwear not fitting true to size or true to your size or true to the size you think it should in no way means that the brand isn't "good." That's just not analogous.
If you meant something else then it's not clear. MP Massimo Piombo is a widely coveted label - especially during its Kiton era. Sealup is another great brand that mostly makes items under contract for other labels such as Burberry etc.
I assure that both companies make great outerwear. You have to be willing to accept that sizing may vary from what's normal for you. Even a brand you already know might have a difference in sizing because sometimes sizing is tailored for the local market of distribution
Embrace the hunt and exercise the return policy if it doesn't work.
I noticed MP pricing had changed and thought they must have switched mfrs. This is first I've seen it "confirmed."
Can you tell us more about this?