Lost Cause
Using spell synthesis arrays had a lot of limitations.
No matter how talented an array master was in their craft, the arrays they created would always fail to synthesize the spell outcomes as well as their original counterparts. And the output was bound to deteriorate with time. Therefore, the production line would only work smoothly when Lensa was there to fix the errors that would pop out now and then.
Mass production of anything is based more on quantity than quality. As long as sufficient quality standards are met, the more products are produced, the greater the profit. Provided there was a corresponding demand for them.
Eren explained everything to the old elf patiently while highlighting the nitty-gritty of two separate projects and two separate products using the same foundation that was Lensa's Ability named Radiant Destruction. He also divided the roles between the two sides equally and offered a 50/50 profit sharing for House Carren.