Is it possible that Rebbi holds that on Yom Kippur there is no difference whether one does teshuva or not? He seems to hold that the korbonos of Yom Kippur and the day itself is mechaper for all Jews. If one person is in shul all day saying al chait and doing his best to do teshuvah and another one stays home and reads the papers can they both possibly get the same kappora? If so what is the mitzva, the inyan and the tachlis of teshuva?
The commentaries discuss your question. The Pnei Yehoshua suggests that even Rebbi only holds that such a person is forgiven for his sins only if he has only done one or two of them. This is based on the Gemara which states that if a person sins once or twice Hash-m will forgive him (although this also seems to be talking about once a person does Teshuva, the Pnei Yehoshua states that it is not horribly difficult to say that this is even without Teshuva according to Rebbi). However, the Pnei Yehoshua states, if a person has more sins than merits, even according to Rebbi Yom Kippur will not help without Teshuva. The Pnei Yehoshua also quotes a Tosfos Yeshonim in Yoma who says that according to Rebbi such a person attains atonement, but only with Yesurim.
All the best,