I have! Poetry is definitely amazing. A while ago I had the misfortune of having to adapt an old Python 2 project with specific system dependencies, a mess of a C compilation pipeline and an annoying set of requirements.txt which made it pretty much impossible to convert (at the time at least), so I would say hell's not over for Python since it's simply been around too long with packaging being in a terrible shape and Poetry can't hope to solve all of it; but I'm sure this is not a problem if you're able to stick to current stuff in a greenfield project or if your brownfield codebase followed some semblance of good practices.

Then again, I would say the same for Node. Modern npm is much better than it used to, yarn 1 is even better (better DX between its CLI design and handling of vendored yarn's), and yarn 2 was magical in the smaller examples where I tried it, eliminating the need for node_modules.

Back on the topic for the SPA problem, I would suggest you take a look at Elm, at least for the learning experience. The Elm compiler ships all the tools you really need to be productive, it's performant, the Elm language gets across the usefulness of its state management model extremely well (unlike React, which is a terrible teacher) and as a bonus it will ruin you forever if you haven't seen functional programming actually being useful before.