My guess (because your question is far from having only one interpretation) is that you propose that the Big Bang theory could result from erroneous interpretation of data due to the failure to consider the possibility that the EM strength has evolved with time. If my assumption is correct, I understand that you refer to the red-shift, that could thus be explained without expansion.
Let us assume your theory does explain the redshift. What do you do with the other major achievements of the Bigf Bang theory ? How do you explain the relative abundance of elements ? Where does the cosmological background come from ?
Plus the fact that, the farther one looks, the jounger observed structures are. There are several unanswered questions about the Big Bang theory, but it occurs to be very robust an hypothesis.