Yes, landlords do the things they do because of capitalism. Their existence is due to capitalism. But that doesn't mean they're not to blame. They choose to be landlords.
Your anecdotal experience of nice landlords doesn't cover the fact that landlords, traditionally, have been bastards to their tenants. There's a reason many countries have had to implement laws like third party deposit schemes and standards for things like smoke alarms, heating systems, etc in rented accommodation.
Landlords are bastards because of capitalism but that doesn't wash away the fact that landlords are bastards.
Okay, but "ACAB" makes sense because even the "good" cops enable the bad system. But how does ALAB make sense? The good landlords are just... good landlords. The landlord performs a useful service by buying and renting out the property which would be too expensive for renters to otherwise have access to. Obviously things would be better if there weren't a need for landlords, but that's hardly the fault of the landlord. What exactly is the (good) landlord doing that is enabling a bad system overall?
They usually invest in property to secure funds for retirement, and to fund kids college, and basically afford life costs. Some actually have a regular job on top of this landlord "investment" thing going on. They mostly fix things by themselves because its cheaper (and sometimes the job is done poorly). Their "frugal" behavior is carried over from their personal lives into their rental bussiness, because they grew up in poverty.
I mean, honestly, its not "landlord bad", its more of "capitalism bad". Landlords exist because capitalism fucks everyone and everyone is trying to get ahead, any means necessary. So some become landlords. I mean, to understand their perspective, they don't view it as wrong because they think "if it's legal, then its okay". That's literally what society tells everyone.
I mean, these "small landlords" won't need to hoard properties if society has UBI, retirement funds that policitians aren't trying to cut all the time, free college, socialized healthcare, people actually being able to afford living, etc.
Direct your anger towards capitalism, taking out your anger on these landlords (especially the small ones) is a waste of time, aim for the politicians and the top 1%.
You seem to be describing most capitalist countries (minus the ubi). The US is the only one without socialized Healthcare. One a the few ones without free college.