I think the 'tradeoffs of the paradigm' are largely inherent in the concept of GIS software that's useful for a ton of different use cases. Digging into just symbology functions showcases this - it's a broad toolset that fits most needs, but I still run into micro-cases where I can't quite get something done (I still struggle with rendering polylines which have ends that touch other polylines where colors/width don't match - ie, an issue with rendering priority. The next comment here is probably going to be pointing me towards a perfect solution).

I assume the issues you find teaching QGIS are also found in teaching Arc, but my last experience with Arc was version 9.x so I'm a little out of the loop.

I think symbology is still not properly solved - even Esri's latest tools (which as far as I'm aware are generally considered to be the best available as regards symbology) are often used only to generate vectors to be imported into something like Adobe Illustrator.

What does esri do that modern qgis does not?

Basically you have increasingly sophisticated symbology and labelling options depending on your requirements. At the top end you have functionality that effectively allows you to recreate a national mapping agency within ArcGIS Desktop (see Production Mapping for more details). If you are familiar with Ordnance Survey mapping this is the kind of quality I am talking about. It's a serious engineering task to put together the toolset and workflows to get anywhere near this. Nothing open source comes close (awaiting OGC true believers..).

That is to say, it's still not perfect, but as far as I'm aware it's near the best COTS option available.