Learn English – Phrase for focusing on unimportant details

We have some CS people on E.SE; what would you call it when someone wants to optimize a two-second process to load data, though once loaded it will be chewed on by an inefficient algorithm for hours?

In a CS context, I'd simply call this "premature optimization". The reason that phrase works is because, in that context, I'd expect most people to be familiar with this famous quote by Donald E. Knuth, or at least to have heard it referenced:

"Programmers waste enormous amounts of time thinking about, or worrying about, the speed of noncritical parts of their programs, and these attempts at efficiency actually have a strong negative impact when debugging and maintenance are considered. We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%."

If I wanted a more colorful term, I might call it something like "painting racing stripes on a tricycle" or, if it's about accuracy instead of speed optimization, perhaps "putting a laser sight on a nerf gun". A somewhat common security idiom would be "putting a vault door on a garden shed" or "a steel padlock on a cardboard box", etc.; the possible variations are endless.

A problem is that this is an idiom within an idiom.

A Google search turns up:

to have a keen eye for sth synonym | English synonyms ...

dictionary.reverso.

and, to give some examples from the internet,

... have a keen eye for pigments and dyes

... have a keen eye for "fabricated" essays

... have a keen eye for details.

but I can't seem to access the promised dictionary.reverso entry.

So 'have a keen eye for' accepts count nouns. 'Have a keen eye for a bargain' is an idiom within an idiom and apparently count.

Have a keen eye for detail is a longer set expression, and obviously uses the non-count version of 'detail'. However, this does nor indicate that 'have a keen eye for details' is in any way wrong.