When we first saw redshift of distant galaxies, the only two mechanisms at the time were Doppler shift and gravitational redshift. Initially, Doppler shift was assumed and so the redshift was attributed to the result of motion.
Then, we noticed redshifts were greater than the value of 1 and so we took the correlation known as Hubble's Law and extracted it from the redshift observations so that nothing had a redshift greater than 1.
Then we took Hubble's Law and said "this is due to expansion of space." This is a huge assumption to make, that there is a new cause just because of the observation of a correlation of redshift per distance. In fact, using Occam's Razor, both expansion of space and dark energy stem from the assumption that motion is the cause. This indicates that, logically, gravitational redshift is the real cause. The question is just a matter of how.
As gravity also can bend light through gravitational lensing, if masses were to be able to be ever larger, then some masses would be so large that they could influence light in our entire observable universe so as to cause it to bend. If that light bent into a Figure-8 pattern as a result, centered on such an object, then it would produce gravitational redshift per distance as well as show how electromagnetic fields are produced by gravity. This view drastically reduces physics by showing electromagnetism as the result of gravity and removing the added concepts of expansion of space and dark energy from the model. The goal of physics, after all, is to find the simplest understanding rather than the most complex explanation.
Just my two cents. :)