Once the four significant domains of life transformation were brought into clarity, I began to see progress made towards them all over time.  I was also curious to develop some kind of unifying theory to connect these seemingly disparate areas.  

The answer, however, had been staring me in the face the entire time: minimalism itself is the unifying thread.  With the decluttering as the main foundation, these other pillars relate as follows:

Fitness:  if you think about it, the main purpose of becoming fit is to lose fat and build muscle for multiple benefits, not the least of which is looking attractive to others and building a foundation for a long and healthy life.  Excess fat is a form of clutter essentially.  It has accumulated on our bodies over time through unhealthy lifestyle choices.  Getting rid of it brings a sense of release in the same way as getting rid of other clutter.  With bodies in excellent condition we can maintain them and look forward to all sorts of possibilities we can do with them.

Finances:  it's not so much about getting rich but being in charge of our money.  That comes through budgeting and getting rid of debt.  Debt is, you guessed it, another form of clutter.  It is a burden to be gotten rid of.  The connection is obvious.  Those people who acquire a bunch of crap over the years in their basement mainly do so with purchases on credit cards or otherwise.  To quote Dave Ramsey, "they buy stuff they don't need with money they don't have to impress people they don't even like."  The inverse of all this can be explained in this article.   Minimalism makes it possible to really be in control of your life.  After all, your life is a business.  The way most people run their lives they'd be better off fired.

Task management:  a  system to manage tasks in a mind-mapped fashion makes things more organized.  One thing naturally leads to another.  This makes use of the principle of habit stacking, as mentioned on p. 71 of Atomic Habits:  the result of accomplishing one task acts as a cue for the next one.  With that it reduces cluttered schedules and minimizes unproductive time.  What we're trying to get rid of here is time clutter.