I do think Ineos have paid some huge contracts for pure climbing domestiques. Wasn't Diego Rosa on 1.5M/year?No, that's not the only reason.
Ineos' budget is big but not unlimited and average budget teams' budgets are lower, but they're not 0. Ineos can't outbid other teams on every rider even if they would hypothetically have unlimited leadership opportunities.
Let's say Ineos have €20m for rider salaries and QS have €8m. Ineos take one big star for €5m, another for €4m and another for €3m. So for their remainding 27 riders they have €8m to spend and QS also have €8m to spend. It means for QS would be able to match or even outbid Ineos for say 1 out of 4 big name riders. Those numbers are made up but you get what's the logic here. After a big budget team commits some of their budget to some of the riders they don't have enough left to outbid other teams on every other rider.