A free for all when all you had to do to get away with murder is point to someone you don't like and say "he's the one that dun it".
Sir Terry put it very well in at least one of his books " the IQ of a mob is the IQ of its most stupid member divided by the number of mobsters "
Also please define "clearly incompetent" given half the time what people complain of as "durr durr dey got let orff" is "the police did not find enough evidence for a charge", or "A jury, having heard the charges and the evidence found them not guilty".
I agree the police etc aren't working properly at the moment, but the fix for that is to actually fund them enough that there are enough trained officers on the beat, enough paid lawyers to push the cases through the justice system and reduce the number of mistakes, enough courts (and judges) to hear the cases, and enough space in the prison cells to hold those found guilty.
Unfortunately that's not as much fun as rounding up a bunch of violent thugs (and typically many "vigilante" mobs are basically organised by criminals, just different ones*), and to out and beat up the people you "think" deserve it.
*Nothing distracts your neighbours from your criminal enterprises quite as much as getting them riled up and pointed in another direction (apparently when the paedo hunter mobs were going around terrorising medical staff and killing a guy who was taking photos of the vandalism of his house and garden, the ring leaders turned out to include a bunch of drug dealers).
So, we'll start with the first point - the ring leaders turning out to be drug dealers. A fantastic advert for our justice system as it stands being ineffective.
I'll answer another point you've made with a little anecdotal story of my own.
I had something stolen. A large something. Something that would have required multiple people and a vehicle. It was clearly identifiable, it had multiple serial numbers on different components. I had photos of it, I had records of each of the serial numbers.
The day after it was stolen I reported it via the police non-emergency system as rather remarkably a colleague of mine found it for sale on facebook marketplace, clear photos showing who it was in possession of, it in their home, in their garden. Impressively the police called me 40 mins later and asked me to supply all the details and photos. I did.
They then took 3 months to attend the guys address by which point he 'no longer had it and couldn't recall ever having had it'. The police left it there until I put in a formal complaint. They then attended his address a second time where he again denied ever having had possession of it. The police closed the case.
I picked up my complaint again and finally 2 months later a more senior officer called me and literally asked "well what do you expect us to do when he says he hasn't got it?". I pointed out at a minimum they could have arrested him on suspicion of handling stolen goods, his response "well we've got no evidence he had it and how did he know it was stolen?".
I pointed out to him that ignorance is not a defence in the eyes of the law and also the photos I'd supplied to them clearly showed it in his possession. "what photos?". Yes, that's right...the initial handler hadn't even passed on the photos. When I sent the photos again and got a response a month later it was "well how do you know it's yours?". I pointed out the serial numbers visible in the photo corresponding with my insurance certificates, that again I'd supplied them. A further month later they'd again attended his address and he accepted he had indeed had it but had sold it and couldn't remember who to or where he got it from.
So that was it, as far as they were concerned they'd made exhaustive efforts and it was case closed.
Throughout this my formal complaint stayed open. It still is. The senior officer that was due to call me back never has despite about a dozen emails and calls to them over 2 years.
Does that sound like competent policing to you?
I know the man that had it. I know where he lives. I know where he works. If I'd visited him that same day instead of reporting it to the police, I'd have my property back.