They probably wouldn’t act as such - after all the Prophet permitted Hazrat Aisha to go and join girls singing and dancing in a wedding celebration but at the same time Hazrat Umar would be very against anything if say this concert was massively disturbing the peace of a neighborhood.
You miss the key point, Muhammad SAW and Umar Khattab RA holds authority, and none of their permissions were for vulgar and immoral dance and lyrics these actors perform today. You really think that Shuhada of Badr would be amazed that Cardi B perform in the Land of KSA and although whole of KSA is not holy but we gotta have respect for the land where Rasool Allah once walked. I am not against people having fun or doing things that blow off some stress, in fact there was a Sahahba in Prophets time who used to play pranks on other Sahabi, and Rasool Allah often enjoy his jokes, but all of them were within the parameter of decency.
If anything, this concert would come tertiary as offensive to these people compared to the excesses committed by ruling classes a few hundred years in Arabia including wealth accumulation, womanizing and crime.
It didn't offend me, its just disappoint me similar to when I see Arabs making tall buildings and wear silk, contrary to what quite literally what Prophet forbade them to do. The world is well within its course towards the great gathering.
In that order of social issues such as leadership failure, corruption and crime this event would be far down the chain of issues to address.
These people may be committing an offense from a personal sin perspective but they aren’t harming another person.
But individual sins even if its done to oneself can not rule out that Fitna and sins spread in a society faster than a message of Good, It took Prophet years of preaching and all he got was handful of supporters from the very low of the society, not that they were low but that is how the society see them as such back. Sin should be discourage whether its done in a individual capacity or collectively, in this regard the concert is out in the open... songs Music of such sorts are something Prophet warn us against. And if we see it from a different prospect this harmless looking concert could do a lot more damage than we expect, have you heard the news of a stampede in a concert recently? people suffocate to their deaths, things like that could and had happen in past.
If anything, I would think it would pain the founders of Islam more to see a country led by corrupt and cruel leadership versus people singing and dancing.
No, A sin is a sin and those who literally died to bring tawheed to that land would not be happy to see Salman khan trying to shake his butt over a song bang bang... similar to that they wont be happy to see corrupt people ruling over, but two wrongs does not make one right... and lets not forget that verse from Quran, "Verily Allah does not change men’s condition unless they change their inner selves" [Surah Ar-Rad (13:11)] if this is how the Awam is, then you get leaders like that as well.
Then how did he manage Hazrat Khadija's business ?
You don't need to be a Phd to run a trading business back in 7th century, He ran her business as a honest man, yes he brought her good profit but does not make him a literate nor the most successful trader in mecca. As I said, tum jaise chawalo se debate kerna bakre ko Gana yaad karane jaisa hai...