The issue isn't whether these hopefuls will succeed but rather...

The issue isn't whether these hopefuls will succeed but rather the claim by SO4 that they have the BEST project. Note I am not saying it is a bad project.
The sum of parts argument is fine but when the only known parts are access to road and definition of a brine of significantly lower grade then the claim doesn't stand up.
Of course SO4 might find from their evaporation trials that they can use a novel and low cost technique to recover their SOP but assuming they don't then I still think they will be pumping more brine into bigger ponds.
That may or may not result in higher operating costs. Bigger ponds will result in significantly higher capital costs assuming similar construction techniques for both miners.
Regarding your comment on pond pilot studies, as you probably know the issue is whether or not in-situ clay can be used as a liner in place of poly. Seepage figures will tell us. If clay is used then the capital costs will come down (or bigger ponds will be built).
As for Lop Nur, they define their resource as % KCl. 1.4% KCl. I presume that 0.8% K2SO4 (SO4) and 1.3% K2SO4 (RWD) are both superior.
SDIC have patented a special process that has a low fresh water processing requirement. This may be a factor in their opex as might the cost of labour in China.
As for operations at Lake Wells and Lake Disappointment I can't see evaporation being vastly different. Lower precipitation might favour LW being further south. The mass of salts harvested per volume of brine from LW will be 2/3 of that harvested at LD, it has to be because the brine isn't as concentrated. If LW operators are to have lower operating costs then they will have to come from processing and energy generation savings in my opinion.