Mainly due to the control they have over iron and for their relic and old town site hunting, they didn't get better depth with the F-75. For their purposes and anticipated depths on buttons and coins and trade tokens and such, the T2 was preferred.
In the long run, "depth" is an often touted topic or claim of performance, but a lot depends upon what types of targets the detectorist i after, the site environment they are hunting in, and what the anticipated results are. If you're only going to recover solid, lock-on Target ID's then you're not going to achieve maximum functional depth with most detectors.
For anyone to provide an educated answer, they would have to be familiar with all models considered and hen compare them at the same sites and on the same naturally located targets to know the difference in performance. All else is simply a best guess or imagination.
Monte