Liverpool are still empty-handed...
FA Cup : eliminated very early
EFL Cup : eliminated in the finale
Champions League: eliminated during last 16
Now there is only the Premier League left to win. We can already call them as the champions here though. Because the gap is 12 points with Arsenal so I don't think even Arteta believes in their chance anymore.

Do you call Arne Slot successful for this year? I think winning a Premier League trophy is a good start at least. He is about to end Liverpool's thirst for this title -
the last one achieved was in the 2019-20 season.
The most obvious sign that Liverpool have already won the title is that bookmakers are not accepting bets on it.
As for next season, it will be a different team - Arnold will leave, Salah may leave, Van Dijk too, etc. It's too early to talk about next season as we don't know what kind of team Slot can put together plus we don't know what the competitors can do.