The majority of these people were not enemies of Putin. They were enemies of Ramzan Kadyrov, the leader of Chechnya, which reportedly has links with Chechen organized crime and generally operates independently from the Russian federal government. Putin is fine with him because he's (relatively) loyal.
Russian opposition and Westerners sympathetic to them tend to blame Putin for their assassinations, despite the fact that Putin cannot effectively control the Chechen government and all the people working for the Chechen government.
That was exactly the claim that was made, though:
Putin's underlings regularly assassinate their enemies in broad daylight (including with gunfire) and nobody gives a shit.
Unless you're arguing that Kadyrov shouldn't be considered an underling, I guess?
He is very much an underling of Putin because everything he owns, all his wealth and his grip on Chechnya is down to honest Russian taxpayer's money pouring into his greedy, corrupt, Fascist pockets. It works both ways though in that Putin does need someone like Kadyrov controlling the province, but in my opinion Kadyrov needs Putin more than Putin needs him. Kadyrov is outwardly loyal to Putin to a fault, even removing his title of "President" and replacing it with "Leader", explaining that Russia only needed one President.
I've argued before that as soon as Putin leaves power, as will happen eventually (all it takes is one big corruption scandal that he can't slither out of), then the Chechen money will dry up and Kadyrov's grip will slip once again, especially if he begins abusing his people even more and becomes more greedy. The only thing protecting Chechnya is, we hope, war fatigue, but give it 10-20 years of Kadyrov's face plastered all over the walls and extrajudicial executions, enforced Islamic law and all the rest of it, maybe young people will be less likely to put up with it.
There are a number on that list however who were not assassinated by Kadyrov or the Kadyrovtsy.