Can’t argue that it feels bad not to be able to progress to the next floor, but the scoring system is fine once you understand how to play the game. Unfortunately, Blizzard thought it would be fun for players to discover how to play the game rather than explain the scoring system with an in-game sign in the Torghast lobby.
You need to go to Wowhead and look up how to earn points to achieve 4-star/160 points and unlock the next layer. Once you’ve unlocked the next layer, you can completely ignore the score as that’s all it’s good for (unless you’re into self-challenge or e-peening to others).
There are also examples of people showing that you can ignore the timer element of the overall score and still get 4 or 5 star runs. You can either go fast and get a good timer score OR you can ignore the timer and focus on bonus objectives (or do a blend of both).