Saying "well you're just less likely to go to the hospital" underplays their importance and gives unnecessary credence to the completely false notion that if you don't get vaccinated the only person you're potentially hurting is yourself.
42% (and even 58%) is still a huge improvement since the article says that the likelihood that an unvaccinated person will spread is around 67%.
The R0 value for Delta is between 6 and 7. So while an unvaccinated person might pass it on to ~6.7 people you will pass it on to only 4.2 people in the beginning (37% reduction), then to 5.8 people (13% reduction).
This calculation also assumes that your chance of getting Covid is the same as an unvaccinated person, which is not correct.
The chances of having a breakthrough infection and passing it to someone else are quite a lot smaller than the chances of getting infected while being unvaccinated and passing it to someone else, just because breakthrough infections aren't that high (Even if they are higher than we'd like).