Worstgen
Cinera
If there's no evidence Rayleigh didn't use penetration haki against Borsalino, then we shouldn't assume he used it. Even the normal barrier haki wasn't depicted, and that was depicted preskip. Rayleigh didn't use a legendary sword either.
Cinera
The sword he used was very nondescript, so it was most likely not a meitou. This also makes sense when we consider that he was a couple of decades into his retirement and wouldn't have been carrying a sword around all this while (he was also about to be sold as a slave, so he would have been disarmed if he had any weapons previously).
Cinera
Furthermore, when he saves Luffy in SA postskip, he's using a different sword (he's come out of his retirement, so he has probably had the chance to retrieve his preferred weapons). Rayleigh most likely fought Borsalino with a fodder marine's sword.
Cinera
Rayleigh didn't use named attacks (Borsalino did) or flying slashes either. You can't credibly make the case that he went all out.