Keep doing what you are doing in refactoring and fixing it. Spend hours on it. Tell the person you spent hours on it. Tell them you expect them it will take them longer, but these are the standards you expect of yourself.
Ask your boss / their boss if they also expect those standards or if you are wasting your time or if this was a good use of your time to spend hours/minutes rewriting this employees work. Ask if that employee should be spending 2x/3x/4x the amount of time on their code to get to that level.
edit: What I mean is, it doesn't sound scathing if it's helpful. Scathing does not have to be in the vocab. Just be helpful to everyone, coworkers and superiors. Everyone wants to do the right thing.
I'd really counsel against refactoring and fixing it, that is not what code review is for, you review, comment and return and leave the refactoring and fixing to the submitter (see above for a more comprehensive solution).
If you insist on refactoring and fixing all the PRs you end up being the bottle-neck, and your co-workers will not learn as much from the experience as they could.
I'd still argue that's probably a good bottleneck to have though, and certainly better than letting the code quality slip. It depends on the timelines and priorities, but I'd rather work somewhere that invests time up front to save time later.
I strongly disagree that the co-workers would not learn from said refactoring. That's very pessimistic on either the coworkers reading comprehension, or pessimistic on their attitude or willingness to engage with the changes without being forced to do so? I don't know I find it amazing when someone offers a refactor suggestion, whatever amount of "doing it" they do for me, I find I learn a lot from learning what the changes actually are. If they do it themselves I get a really good feel for their style and what I can learn from it.
edit: And on the flip side, I find it's sometimes faster to just make a small refactor change than to explain it in person --- but this depends on the physical locality of teammates and schedule conflicts. In other cases it's easier to swivel the chair around and poke them on the shoulder and explain the refactor than to make it. Which is easier depends on priorities, chain of command, schedules and all that.
Ask your boss / their boss if they also expect those standards or if you are wasting your time or if this was a good use of your time to spend hours/minutes rewriting this employees work. Ask if that employee should be spending 2x/3x/4x the amount of time on their code to get to that level.
edit: What I mean is, it doesn't sound scathing if it's helpful. Scathing does not have to be in the vocab. Just be helpful to everyone, coworkers and superiors. Everyone wants to do the right thing.