The way I see it, at least for individual / non-corporate owners, many of them are having their own struggles through covid-19. I would not assume every landlord is sitting on a property empire and passing their days eating cakes at Lady M. Similarly, I would not assume every tenant has taken a pay-cut or lost their job. Some tenants are genuinely enduring difficulties and I would like to help them. For those simply having a go at a reduction, I may react differently.
But of course it's a renters market now, and you have every right to try. As both tenant & landlord, i've not personally asked for a reduction where I live, but have been asked for one by more than one party.
In considering, i'd look at whether the rent was cheap to begin with. Unlike some landlords, i'm not in the habit of jacking up the price at each renewal; I believe a good relationship should go both ways. Financially, a rent reduction is surely preferable to an empty apartment and agency fees of course... my issue is that tenants obviously never complain if they're underpaying vs. the market. At some point, when it borders on taking the piss, i'd be inclined to say good riddance as a matter of principle.