What to do after the 23k traditional limit

I am lucky enough to max out my traditional 401k up to the 23k limit but still have some income to spare. My company allows for a mega backdoor Roth so I could contribute to my Roth IRA still.

My only concern is that if I pay 24% in federal taxes now (marginal tax rate), wouldn't I need to have an effective tax rate greater than 24% in retirement to make it worth it (pay less later than now)?

Given I already maxed out the traditional is it worth it to still invest in Roth even though I won't save taxes on it (just free gains)? I could just use the roth as a personal savings and pull our the principal if I need it but the gains would be stuck there.

The alternative is to just put extra money into a personal savings account which I could maybe use to buy a house in the future (23 years old right now).

Please correct me if any of my calculations seem incorrect and any advice would be appreciated.