So it's a good strategy still, it's just that most of the time you can improve your deck faster by adding good cards than by removing bad ones.
If you add powerful cards the power of the deck increases, but if you remove weak cards it also increases, and the consistency increases further: if you have 15 cards 10 of which are starter every hand will average 4 starter and 1 new card, but if you have 10 cards 5 of which are starter it’ll be split 3/2 ou 2/3 on average.
This is also why Snecko Eye (the relic that gives +2 draw every turn and randomizes card cost) is arguably the best boss relic. Even if you only get to play one 3 cost card, it's more likely to be the best card in your deck.
I can't agree with this. Snecko Eye is very strong, but playing a 3-cost card will cripple you. It's strong because you draw a lot of cheap cards -- the lesson of Snecko Eye is that playing several cards is better than playing one card, even if the cards you got to play were chosen randomly.