Here is an explanation of the situation.
"Rhythm" refers to a "repeated pattern of movement or sound".
In the context of osu! this usually means the player keeping rhythm with a constant tempo.
When a song maintains its tempo, circles and sliders are used to create what you expect: a map that requires the player to maintain rhythm while moving around on the playfield.
https://twitter.com/ppy/status/704995374998552576
When a song's tempo changes, however, the rhythm is thrown off. The music and rhythm are no longer the same thing.
The player has to adjust to the new tempo somehow, but there is no time to do so. Tempo changes come without warning.
Sliders are often used to keep gameplay fair to the player during these tempo changes.
It lets the player stop following the previous tempo and prepare for the new tempo without unfairly punishing them.
You can't click circles to the beat when the beat keeps changing.
https://twitter.com/ppy/status/705035574248235009
People don't use sliders to make rhythm pointless.
If that were true, then they would never use circles in the same map!
Instead people combine the two.
Circles and sliders when the song is consistent in tempo, sliders when it isn't.
https://twitter.com/ppy/status/705037389140328448
This rhythm game is far more fair to the player because of it, though.
This use of circles and sliders makes this game compatible with almost all kinds of music as well.
Here are some example maps that rely on this to function properly.
https://osu.ppy.sh/s/412938
- This map is OD 8 and consistent BPM, it requires good accuracy to do well in. The intro, however, has many BPM changes that gradually slow down. It would be unfair to force the player to hit these objects properly, as there is no rhythm the player could follow.
https://osu.ppy.sh/b/453358
- This is a bundled map. It has moments where the rhythm switches to 1/3 without warning. The mapper keeps the gameplay fair by putting those moments of 1/3 into sliders. In this situation, it would be unfair to ask the player to magically know the objects are 1/3.
https://osu.ppy.sh/s/65994
- This map has 280+ tempo changes. Sliders are used in harsh tempo changes, and circles are used everywhere else. This sort of map would be impossible to create in version 2.
So, in summary, the game is already a real rhythm game. Circles exist. Circles are used.
Sliders are often used as a tool to avoid having this real rhythm game be unfair.
Forcing sliders to have accuracy wouldn't make the game more of a rhythm game.
It would simply prevent perfectly good songs from being mapped.
Tempo changes in maps would be ruined.
There is no benefit to this.
"Rhythm" refers to a "repeated pattern of movement or sound".
In the context of osu! this usually means the player keeping rhythm with a constant tempo.
When a song maintains its tempo, circles and sliders are used to create what you expect: a map that requires the player to maintain rhythm while moving around on the playfield.
https://twitter.com/ppy/status/704995374998552576
When a song's tempo changes, however, the rhythm is thrown off. The music and rhythm are no longer the same thing.
The player has to adjust to the new tempo somehow, but there is no time to do so. Tempo changes come without warning.
Sliders are often used to keep gameplay fair to the player during these tempo changes.
It lets the player stop following the previous tempo and prepare for the new tempo without unfairly punishing them.
You can't click circles to the beat when the beat keeps changing.
https://twitter.com/ppy/status/705035574248235009
People don't use sliders to make rhythm pointless.
If that were true, then they would never use circles in the same map!
Instead people combine the two.
Circles and sliders when the song is consistent in tempo, sliders when it isn't.
https://twitter.com/ppy/status/705037389140328448
This rhythm game is far more fair to the player because of it, though.
This use of circles and sliders makes this game compatible with almost all kinds of music as well.
Here are some example maps that rely on this to function properly.
https://osu.ppy.sh/s/412938
- This map is OD 8 and consistent BPM, it requires good accuracy to do well in. The intro, however, has many BPM changes that gradually slow down. It would be unfair to force the player to hit these objects properly, as there is no rhythm the player could follow.
https://osu.ppy.sh/b/453358
- This is a bundled map. It has moments where the rhythm switches to 1/3 without warning. The mapper keeps the gameplay fair by putting those moments of 1/3 into sliders. In this situation, it would be unfair to ask the player to magically know the objects are 1/3.
https://osu.ppy.sh/s/65994
- This map has 280+ tempo changes. Sliders are used in harsh tempo changes, and circles are used everywhere else. This sort of map would be impossible to create in version 2.
So, in summary, the game is already a real rhythm game. Circles exist. Circles are used.
Sliders are often used as a tool to avoid having this real rhythm game be unfair.
Forcing sliders to have accuracy wouldn't make the game more of a rhythm game.
It would simply prevent perfectly good songs from being mapped.
Tempo changes in maps would be ruined.
There is no benefit to this.