Depends on what you mean by "better". If your goal is to reduce gun ownership, making it legal won't make it better. If your goal is to reduce violence, making them legal might make it better. Many of the reasons for that have been cited before.
You have a singular focus on reducing gun ownership instead of the actual problem - which is violence. I do not understand it. I think you want to help reduce violence, but your continued substitution of gun ownership for violence calls that into question.
Taking the drugs and prostitution examples for a moment, legalizing them won't decrease the amount of drug use or prostitution use (the illegal form of which is called human trafficking, which sounds a lot worse). So if your goal is to decrease usage, legalizing it is not a good idea. If your goal is to reduce harm associated with those activities, legalizing it might be exactly what is needed. Because making drugs illegal results in a lot of unwanted side effects, like guns used to protect drugs (because cops can't be called), and drug deals in cash (resulting in armed theft), and drugs cut with dangerous substances (because you can't check yelp for reviews), and more dangerous overdose situations (nobody wants to take you to the hospital). Same goes for prostitution. Pimps become important when johns can abuse the worker without fear of reprise from the cops. Pimps can then abuse the workers also without fear of reprise from the cops. Prostitutes are also more likely to carry dangerous diseases (because you can't check yelp for reviews), and guns are also needed to safeguard cash transactions which are vulnerable to theft.
So, as you can see, your priorities are quite important. Yes, if your goal is to reduce gun ownership, legalizing it doesn't help. That shouldn't be your goal, your goal should be to reduce violence, and making them illegal doesn't necessary achieve that goal.