273 Stroker, 4.00" Crank
For performance, the 273 is a boat anchor - especially when 318s are almost free and look identical on the outside.
Everything else you said was true. But the 273 is nothing like a boat anchor. On the contrary, the Commando version is more like a mini 340 -- high compression, high revving, high HP/CID ratio.
But you are absolutely right about a 273 stroker -- it makes no sense and wouldn't achieve anything. The valve and port sizes on a 273 are perfectly fine for 273ci, but are too small for a larger displacement -- that's why a stock 318 is not a hot performer (larger bore, with the same small valves and ports). Adding displacement via stroking would make the breathing restricted (relative to the cylinder volume), with no way to fix it given the small bore. Stroking usually adds torque, but you'd be choking it at the top end, so probably no net gain, and a serious loss of area under the curve.
IMO, the 273 4bbl was pretty much optimized for a production engine of that displacement. It's hard to improve its performance significantly without major changes. and the best way to improve the performance of the 2bbl low compression version is to imitate the factory 4bbl configuration. If that's not enough for you, then yeah, you need to look for a larger bore block, 318 or 360.