Personnel people are so important in the NFL because, like you say, you cannot just plow money in to the team. They have salary caps, revenue sharing, and a decent amount of control over player contracts (franchise tag, restricted FA, ect.).
So RL's failure in Cleveland had much more to do with who was hired than how much money he spent. That being said, most people viewed the Mike Holmgren hire as a good one and it has not worked out. Do not think you can blame someone for hiring a guy most other teams would have hired as well.