OK; I’ll roll with that for a while. If I accept your premise that continuity with past D&D games is a core restriction, then maybe you could say 5e does a pretty good job within that space. Maybe there’s limits to how good you can make a D&D game without most of the playerbase complaining that it just “isn’t D&D”.
If so, then one might consider D&D an analogy for C++ among programming languages. The design decisions behind it make no sense at all until you realise that the entire fucking language is a matter of historical contingency and path dependency; in that context it’s honestly surprising the strides that have been made with C++11 and C++17.
Yet, as with D&D, it’s so easy to envisage better if you step outside those historical strictures and look at the broader design space.
See, if the case for D&D boils down to continuity with the past, then there’s a fundamental issue: why should new players, who don’t have any attachment to D&D past, be exposed to D&D present? Why should the chains of history be imposed on them?