The mmo is a moderatly strong solvent. Since you have been using this practice for some time the engine internally is probably as clean as it is going to get. So no benefit likely by continuing.

You could put a quart in the fuel tank with a fill up to clean out your fuel system now for awhile. Make sure to carry extra fuel filters and the tools to change them though just in case a lot of junk is loosened up.

Since I cannot see the by products of combustion actually weighting more than oil. Although perhaps they could. I might assume their accumulation in the oil filter is reducing the ability of the oil to flow out of the filter as fast as a less unobstructed one would when changing it. So more oil is retained in the filter much longer and it seems heavier .

This is just a guess at best but at least some hope for your feeling the oil filter seems heavier since you started using the MMO in the base oil. Some engines are indeed crudded up internally pretty bad.