legacy software full [of?] a truckload of arcane commands & flags with bad defaults

You need to learn about xargs. It'll make you cry. But when I needed to properly parallelize a RHSatellite run - wow is pulp ever a bag of shit - so it would finish in under 9 hours and not trip over itself with 105 (no shit) different repos, it was integral.

There are three different kinds of regular grep, and they have incompatible command line switches.

I'm not gonna list the plethora of tools with arcane and/or lengthy option lists, but I do wish I could impress upon you the idea that every tool evolves , and evolution is usually coupled with growth and specialized additions.