It's interesting how staunchly people will defend "standard Western musical notation" but I agree with you - from a design point of view it looks like notation originally designed to match a piano keyboard which has then had many years of extra features inelegantly bolted on to it. It works well enough for the keys of C or Am but gets progressively more ridiculous the further you depart from those keys. And transposition is a mess.

Some people seem to think that standard musical notation is "right" and you can't possibly have any alternative notation and yet this is clearly false. There are at least two or three alternative forms of musical notation in wide use today. Most guitarists use tablature notation because it's better suited to that instrument - standard musical notation is less useful on guitar since it doesn't clearly capture the different ways that a single chord can be played. So it makes sense to have a special notation for that instrument.

Secondly chord charts are used by musicians everywhere because they're very concise at conveying the chord structure of music and often that's all the information you need. Standard notation is just way too much information in that case.

The third, less commonly seen form of musical notation is just like the one you've described. It's seen in video games like SingStar[1] and in modern music composition software such as Ableton Live[2] and others. It's used so often in music composition software because as you've noted it's very intuitive and far less cumbersome than standard musical notation. Transpositions become trivial and everything just makes more sense.

[1] https://www.gamesmen.com.au/media/catalog/product/cache/1/im...

[2] http://whereisdarran.com/wp-content/uploads/2014/02/Screen-S...