Well, I see you made clear you really like Total Commander. However, I am giving my testimony on a freeware software that I think, in my opinion, is my favourite file manager (the original subject of the post).
I come from years of paying and using Powerdesk Pro in my systems, but I had trouble with their new owners (Avanquest) and decided to move over to something else. I tested several explorer substitutes and ended up landing on FreeCommander years ago (2009 if I am not mistaken) - I do not regret.
I do like Open Source, but when someone has developed Total Commander for for over twenty years, and has made it completely uncrippled shareware for all that time, I like to support the author.
Technicalities, technicalities... Freecommander is closed source but freeware.
Well, I am also supporting the author by advertising what I think is his very stable and decent product created only with donations and word-of-mouth advertising. This is a practice also done by one well-known aussie that runs this server...

I have paid for my license.
Well, just because Freecommander is freeware it does not mean the software is not good or does not deserve to be advertised in a public forum. I know a lot of paid software that is simply not good when compared to open source clones. But again, one scenario is not applicable everywhere.
Every time I have tried the clones, I just do not find them as good. They do not feel as solid, and they usually are missing some tools I use all the time. I just do not trust them 100%.
In the software landscape there are too many levels of quality and features that appeal to different users. Also, good or not good is a matter of opinion, it is just my favorite file manager. I agree with your impressions about opensource, but they are also applicable to freewares, ad-based freewares, sharewares, commercial...
I have done a lot of IT support work, and Total Commander is usually the first thing I install on a new system (or run from a USB stick if I cannot install it).
I do the same with Freecommander... Again, it is a matter of opinion.
I don't use file managers with Linux. In my opinion, it is too much hassle.