Embedded in this view--to me--is that you may view justice more as punishment of the offender, and less as protection of society. Again, not a 'wrong' view, but consider, in respect to your slap/steal wallet scenario...
• What if the person who only stole the wallet is well known to police for many, many previous crimes--and not just petty crimes--and that person is unrepentant in court, claiming he has a right to take what he wants, when he wants it.
• And what if for the person who slapped the doc man AND stole his wallet, this is their first crime ever. This person weeps in court, expressing such remorse at his own actions, and it comes to be understood that had recently lost his job because of insane tariffs, and ICE agents had recently shot his wife in the leg, and his children were going hungry. He committed crimes against his better judgment and under extreme duress.
I think justice should not be a strict accounting of retribution for damage done. It should be a much more nuanced balance of circumstance, intent, remorse (recognition of guilt), and likelihood of re-offence. Justice should ask, who is the offender and what course of action in sentencing is most likely to produce a beneficial outcome in respect to the overall needs of the society.
Concurrent sentencing allows a court to both honour the structured legality (the offender was found guilty and properly sentenced on all charges), and the best interests of society (the offender was deemed a low risk to re-offend, and that prolonged incarceration would compound social harm, not remedy it).
What is justice with no possibility of mercy? Maybe think of concurrent sentencing as a legal mechanism for a court to show mercy.