“Keeping” ist not the point. It’s no news that you can “keep” Paros in normal or big or huge tanks. The whole intention of the Parosphromenus Project is to propagate the seed of a new thinking in the aquarum hobby, especially if fish are concerned that are threatened to extinction by the nearly complete destruction of their habitats. We do not need such fish for decorative aquaria.
From an aquarist point of view, these fish are not for keeping them but for participating in sustaining them. The proposal to use small tanks is led by the overall aim to breed them. And a 54 liters tank is still a small tank. Of course, you can breed Paros very well in such tanks. I have nothing against them. But you might tend to change less water. And that is not helpful for blackwater fish or the fight against Oodinium.
For me, the lesson of Marcin means probably: In a huge tank of 640 liters the milieu for Oodinium is much less favourable than in 10 or 50 liters. But it’s no useful recommendation for most people.