Transaction cost has certainly not been “the same.” Your reference to bytes suggests you’re referring to Transaction SIZE? Maybe. Cost, no. Cost, denominated in SATS has gone DOWN over time. Cost, denominated in DOLLARS has gone UP over time.
If the size is the same and the fee rate is the same, then the sats cost must also be the same. The only way for the sats cost to decline, is if the fee rates decline (most people are expecting the opposite) or forks that create new efficient methods of using blockspace (SegWit, Taproot)