“But the very strong Minhag is to be Oser.”
If it is minhag, it isn’t asur. There is a difference.
“It doesnt obviate hundreds of years of psak limaaseh and mesorah though.”
Can an acharon can ignore other acharonim? If you can pasken halachah l’maaseh based on chazal and rishonim, you can get very different conclusions. The Vilna Gaon did just that, and to a great extent so did Rabbi Joseph Soloveitchik z’tz’l and Rabbi Ovadia Yosef z’tz’l. Given our strong idea that earlier authorities are greater than later authorities, it takes a lot to say that the Bavli, and a significant fraction, possibly even a majority, of the important rishonim, can’t be followed.