For what purpose are we talking here? For modern viability? It is a hard thing sometimes. Powerful will always be powerful, but there can be things that just are better that pushes it out.
A good example is storm. It is a very fast combo deck that is very consistent.
It isn't played that much right now because there are better things to do in modern.
It doesn't mean storm is a bad deck.
If you are in the spot where you want to get into a deck, but don't know which one, start to learn what archetype you want to play.
It is not easy to figure this out, so the free thing you can do is find someone who is streaming the deck and see if that is worth watching.
If you get bored watching the same deck in 10 different 2 hour streams, then ask yourself why you even want to invest $1000 in it?
When you think you have figured out what style of deck you want to play, start by collecting the expensive pieces that is shared among most decks.
I don't know what you like, so let's say you have fallen in love with 8-rack and you want to make it your first modern deck.
There is a budget version and a non budget version and it makes sense to start with the budget version and then get the good stuff as you go.
Don't go too far into this idea.
Don't buy a ton of duress (and pay shipping for a bulk common) when you want thoughtseizes.
Substituting Liliana makes sense as she is very expensive, but she is not a card that is likely to ever get banned, she is played in other decks and she holds value well.
Let's say after a year or two you get tired of playing 8-rack, you can start to shop around to see what other decks could be fun to play.
You could go into lantern, keep the hand disruption and the bridges. If you experimented with a blue or green splash prior, you could easily make that transition as the new big investment is the moxes.
You could also go into jund instead if that works better with your playstyle.