The problem with 76 1:1 and TMax is that it produces a sag in the middle of the curve, and hence a relatively longer upswept toe instead of the intended steep toe. So to get better deep shadow gradation, you either need to get the exposure higher up the curve with a bit more exposure via lower ASA rating, or switch to a more compatible developer. The original version of TMax could be finicky about overexposure, however, and the curve could shoulder off prematurely. Staining pyro developers helped that. Subsequent tweaks to the emulsion, along with today's excellent VC papers, have made life easier.
Plus X was engineered for the studio portrait trade, and was classified as an "all toe" film with a very long upswept curve favoring highlight reproduction at the expense of shadows. Developers like D23 went along well with that kind of application. Kodak, introducing TMax, planned it as a silver bullet film due to its versatility under different kinds of development - replacing Super-XX for long straight line applications like color separations using certain developers, replacing Plus X Pan using a different development style, replacing Tri-X for photojournalistic purposes in a middle of the road sense. But it was hard to teach old dogs new tricks, and the very versatility of TMax equated to greater fussiness if you weren't aware of the necessity for quite specific development recommendations which many weren't accustomed to. That's still the case.