"But it is unclear if firms’ profits need be so high to sustain research." It's very clear, and they don't. Profits are enormous. Profits are also calculated a

"But it is unclear if firms’ profits need be so high to sustain research." It's very clear, and they don't. Profits are enormous. Profits are also calculated after the cost of R&D. So no, profits don't need to be astronomical for companies to still be profitable after the cost of R&D.