"Not pivoting to an adequate backup plan" means exactly what it says. The problem wasn't the pursuit of Ohtani/Soto, it's that they didn't do anything once those pursuits failed.
I see the Plan B options as individual failures completely unrelated to the pursuit of Ohtani and Soto. I don't think it's that complicated. Who did they miss out on while they were waiting on Soto? Tyler O'Neil? Sure! Maybe Adames too, I guess.
None of the other bats (Teoscar, Walker, Pederson, etc) signed until weeks later. Some are still available.
The same happened last year, where Ohtani was one of the first players to sign and there was still tons of time for them to address the problem.