Steam/No Steam; Fan/No Fan; Steam B/f vs Aft....theory????

I've searched for the subjects quite a bit, by reading blogs/articles and watched videos about it.

I do understand the BASIC principles about using steam at the beginning of baking helping the oven spring and preventing the crust formed too quickly, such as sourdough boule or just basic artisan bread with steam for the 1st bake and finish up without to brown it.  I just don't understand why steam would make crispy crust???  (Chinese steamed buns are all 100% steamed without dry air, Artisan bread crust gets crusty because of the DRY Baking on the second bake changed the jell molecule, right???

Nevertheless, I am very confused about most soft crust buns, rolls, or sandwich breads are baked WITHOUT steam at all!.  Isn't it contradicting the idea to form the crust quicker with harder crust without steam????

Chinese steam buns are steamed from the beginning to the end of the cooking process, and they are super soft in and out (I am hesitant to use the word "crust" for the outer skin of the steam buns, for they are NOT crusty at all).  Having this concept, isn't it all the best to just using 100% steam while baking buns, rolls, and sandwiches?  To me, it seems to be, for both my husband and I have weak teeth and prefer softer bread and crust.

Q1. It doesn't matter which recipe I use, all of the crust of my sandwich bread, rolls, and buns are NOT as soft.  Thus, I learned some tricks online to covered them with damp towels while they cool down after being taken out from the oven.  This truly helps soften the crust, yet it's not ultimate (it's like once the damage is done, it's hard to reverse it).  For my purpose and liking, does 100% steam for the entire bake serve the purpose of soft but brown the crust???  If so, why most of the soft crust bread are not baked with steam at all?  I'm buying a combo steam convection oven.

I focus only the steam and temperature from some recipes below to compare:

Shkupan sandwich      350F    Steam N/A

Classic Sandwich        392F    Steam 60%   (1st bake)

                                    392F     Steam Off    (2nd bake)

Challah from Babish    392       Steam 60%

                                     360       Steam Off

Traditional Challah       350       Steam 60%  bottom rack

                                     350       Steam 60%  top rack

Dinner Rolls                  375       Steam 100%

                                      375       Steam Off

Hamburger Buns           350        Steam 100%

Hot Cross Buns              325       Steam N/A

I understand that I cannot just look at the temperature and steam for comparisons, but every recipe process and each ingredient affect the outcome.  However, I excerpts those recipes with very similar process and ingredients with similar percentage of ingredients and similar baking time.  Anyway,

Q2.  I just want to KNOW the THEORY behind the above examples.  They all yield for SOFT crust.....

The only thing I can gather is that the higher the baking temperature goes, more steam is needed, whereas the lower needs less steam or no steam.  Is that right?

 Almost always, if steam is called for, it's for the 1st bake.  However, I saw also a grilled cheese sandwich in oven, as well as toast recipes, starting out with dry bake and then steam later to get both crunchy and chewy texture. 

Q3. what's the different result between steam 1st and then brown vs. bake dry 1st and then steam?  They all seem to be the same result to me????  What's the theory behind steam 1st or later?????  I would assume dry bake 1st and then steam would make the toast soggy, but nope.  it's the same as steam 1st and then dry bake.

Convection helps air circulated better and shorten the baking time, BUT

Q4. If I want softest crust for any kind of bread, should I just leave the fan out?  We all know that air dries things out!

Thank you in advance for your input