The welding arc is a very complex phenomenon.
You should make a difference between an arc in wich metal is transported (MMA, GMAW, ...) and a true electric arc (GTAW).
Penetration, heat distribution etc. describing the GTAW arc is totally different compared to a MMA or GMAW arc. An arc in wich metal drops are transferred, there are also magnetic forces around the metal drops, causing penetration once they are projected in the weld pool !
In other words : you can not explain the difference in penetration between GTAW (DC- causes penetration) and MMA/GMAW (DC+ causes penetration) based on heat distribution generated at each electric pole.
If you want to know all details, look for welding physics handbooks !
There's even a contradiction :
(1) Tungsten will give penetration on DC- and will not melt
(2) a wire will give penetration on DC+ , but if you want a high deposition rate, you should make it DC- (wire melts, tungsten not) ...
Conclusion : it's all about physiscs , there's no such thing as a welding arc , every arc has its little differences resulting in strange conclusions.
Also generated gasses in MMA, shielding gas in GMAW will have an effect on the characteristics of the arc !
It's so complex to describe.
Stick to the rules of thumb and try something to raed about arc physics. I am not sure you will get any smarter ...it's very boring stuff.