MineraExar - the Brine JV between Ganfeng & Lithium Americas...

MineraExar - the Brine JV between Ganfeng & Lithium Americas (LAC) - is currently well under construction however in September they revised the development to increase not reduce production by 15000tpa LCE to a total of 40000tpa LCE. So to be clear this brine producer has not reduced production output and is yet to be a producer.
LAC is also trying to develop a clay based (not brine) lithium project in the US that the article you linked to, however it is not yet even financed and project economic feasibility of extraction from clay is still questionable. They have announced a reduction in the size of the development.
Projected Opex increases are a combination of aiming for a higher proportion of BG product and adjustment to Opex figures that occur with every lithium project as they get nearer to or enter production.
PFS Opex projections are an industry joke and bear little relation to actual real world costs once commissioned. This applies equally to brine and hard rock PFS estimates due to competition for funding.
This is why there are so many lithium projects under development that claim to be the world's lowest cost producer. Nemaska lithium is a prime example of how PFS / DFS numbers are overly optimistic as each new proposal needs to appear financially more attractive than the competition.

There is plenty of room in the market in the medium term for hard rock, brine & clay sources.

Also a reminder for all the hard rock investors that jump on the bandwagon of Argentinian brine producers wasting precious water - the vast majority of water usage is brine with minimal quantities of industrial ground water. They are not wasting drinking water and even a fifth grader understands that if brine is evaporated in a high altitude desert it will precipitate as clean water over the mountains. It does not disappear into space and the brine operators are not diverting rivers or impacting farmers because the brine is of no use to them.
Final point to consider is the level of water stress at the brine operations. SQM & ALB operate in a highly stressed region - Salar de Atacama - that extracts brine from the same location as the world's largest Copper mine - Escondida - extracts fresh water. There is also competition for drinking water from the Atacama basin. On the other hand, the Argentinian brine operations are located where there is no other significant competing interests for the water from their respective Salars. I have highlighted their locations on this map that demonstrates geographical water stress risk.