Hi Lizard king,
Good to meet another coffee enthusiast! If I may add to this or amend this, while there are many factors affecting crema some of which you've covered, properly roasted coffee has nothing to do with how much crema is generated. Volume of crema is mainly a sign of freshness of the roast and varietal of bean among other factors including brewing like you mentioned. You can badly roast coffee and if its fresh you'll still get crema but badly balanced flavours and not the flavour profile you were aiming for. Stale coffee just won't generate crema cos the carbon dioxide has degassed completely. Certain arabica bean varietals will generate more crema and Robusta will generate more crema than Arabica which is also one of the reasons why its used in espresso blends.
I know you don't regard robusta as coffee, but Indian Kaapi Royale robusta is highly regarded worldwide as well as robusta from another Asian country I forget but was it Vietnam? Also Mysore Nuggets and Monsoon Malabar are world renowned.
Regards