Should this be implemented in endpoints at all?

Congestion control is far from a solved problem, especially not across wider, less-controlled / uncoordinated networks. Some say ECN is the magic bullet, especially in its recent updated form of L4S / TCP Prague. Others (including a regular commenter here on LWN on networking matters, and Linux congestion/buffering contributor) I think disagree with that.

Congestion control is a bit easier on low-hop, tightly controlled networks - i.e. DCs - but even there it is not solved. Fairness across different kinds of CC in particular is a bitch, as is fairness across flows with very different RTTs and/or BDPs. E.g., congestion controller might work great competing with low-latency, fast connections (i.e. intra-DC), but have issues with fairness competing with flows with different properties, like much higher RTT (e.g., cross-region DC to DC). It's clearly not at all an easy problem.