Daas Yochid:
1. Look at Radvaz on that Rambam in Shemita Vyovel where he clearly says the Rambam there is not contradicting his harsh words he says in Talmud Torah about people who make parnassah from Torah rather his intention is the “Lo shevet Levi bilvad” will have Siyata Dishmaya in their work for parnassah and earn enough to free up their time to learn Torah.
2. The point about Rav Moshe in the Tshuva is that he is clearly going with the pashut pshat in the Rambam that the one who learns and works is the HIGHER Madrega and not the other way around.
3. For you to throw such a severe Rambam in the garbage by throwing out a reckless “We don’t pasken like that” is Ziyuf Torah as I said. I wouldn’t exactly compare this Rambam to paskening like Beis Shamai as you are suggesting… A careful reading of the Kesef Mishna you quoted will show the opposite of what you said in his name, all the Kesef Mishna does is defend people who do earn money from Torah Learning.
The Biur Halacha can be understood just as the Kesef Mishna, (although I can see in the words of the Biur Halacha how one can misread them as to be arguing on the Rambam as to what is a higher madrega) merely providing a HETER for those who wish to go AGAINST the Shulchan Aruch and Not got to work.
To go against the simple reading of Rov Rishonim, Tur and Shulchan Aruch along with many Achronim on the basis of your understanding of the Biur Halacha is Megaleh Panim Batorah Shelo Kehalacha.
4. For some reason none of your “Poskim” decided to change the tefillos we say at the most critical and holiest times of the year (Birkas Kohanim, Hotzaas Sefer Torah Yomim Noraim, Birkas habanim Erev Yom Kippur) which ALL ask Hashem at length for blessing in PARNASSAH that will enable Avodas Hashem.