I think people sometimes overestimate how well funded JFR is these days. They are still a large organization and have many institutional advantages from decades of running multiple cars and having many of the best minds in the sport as part of their "brain trust" at one time or another- their library of parts, data, and research is vast. But in terms of actual cash outflow, I think JFR has to run a pretty tight ship.
This isn't the glory days of Castrol and Ford and AAA- while they are nice sponsors and their support is appreciated, I doubt companies like Peak and Cornwell are coming close to the (inflation adjusted) dollars JFR used to get. John is somewhat unique among modern teams in that he became wealthy by being a driver and team owner. The race team IS his business and source of his wealth, so unlike most other owners he doesn't treat it like a sideline. The numbers have to work, and expenses have to be controlled to align with revenue. Unlike 20 years ago, JFR probably doesn't have the fattest checkbook in the pits when it comes to personnel.