Interesting, I'd never really thought about it in the way the OP describes.
That seems like one possible weakness for a weaker player, but there are others, such as:
1) Pet cards
2) Not including enough econ and draw (especially on the runner side)
3) Trying to do too much, eg, a fast advance deck that also plays with tags, tries to kill the runner and shoot down their rig
4) Not considering matchups against common archetypes
5) Only thinking about the best case scenario, not the average case
6) Not considering opportunity cost, eg, when you put a card in the deck, the question isn't just whether it does something useful, but whether it's better than any of the other cards you could have included instead
Yes, having typed it out, 1 and 6 are very similar.
I think I became a better deckbuilder just by thoroughly playing with some of the popular archetypes at the time. I started playing just before Upstalk came out (which contained NEH), but I only actually started playing NEH some 3-4 datapacks later. Until that point, I'd played alot of HB, dabbled around with basic scorch kill and PE kill, and then made a Tennin fast advance deck - when I played a bunch of games with NEH fastrobiotics, it became obvious why it was streets ahead, and gave me a better understanding of how it can lose.
I think there's nothing wrong with being original in deckbuilding and wanting to go your own way, that approach can be successful at all levels (Timmy Wong is a good example). But to do that you first need a solid grounding in whatever the mainstream decks are at the time. Just hearing about how a deck is meant to win doesn't give you that: we all know CTM wants to overwhelm the runner with powerful assets, score breaking news into (tag punishment) and try to cover the runner in tags, but only playing the games with and against gives a good understanding of the typical decisions you'll have to make.
That's how I think I turned the corner anyway, others might have different experiences