I think you are out of touch with the typcial struggles of a Polish household. In fact if you ask bankers and economists raising a deposit is a major issue - when the banks wanted 10% or sometimes 5% maybe not a problem but if they start to look for say 15% then it will be out of reach for most.
To be honest, if they can't raise 15%, then they shouldn't be buying a flat in the first place. I would be all in favour of raising it to 20% - yes - it would mean home ownership would decrease, but look at Germany - renting is common there and isn't seen as an issue.
One of them runs a modest car
And he's paying nearly a thousand a month to run it - so he should drop it. If a car costs you 1/6th of your income - it really is time to give it up.
Most Polish cities - it's about 80zl a month.
So - we've already worked out that they can save about 1000zl a month easily.
And they could easily buy a flat in a satellite town - take Poznan for instance. There are plenty of decent flats available in places like Szamotuly, Oborniki, Wresznia, Srem, etc - for around 150k for a good sized, modernised flat. Train to Poznan is about 250zl a month, and takes around 30-40 minutes. Given that vast amounts of people around the world commute for 1.5 hours (look at London - 2 hour commutes are normal) - what's the issue?
Much of the problem is due to people wanting only the best and not being willing to work hard enough to get it.
Throw a child into that equation (which for many is the catalyst for wanting to buying instead of rent and you can surely see it is a huge problem.
Actually - this is interesting that you mention this. I think, honestly speaking, this is what breaks many Polish couples - women have a desire to get pregnant as soon as possible here, and I've seen several couples where they've let the hormones take over - and as a result, they'll probably be forever renting.
Sorry, but there's no right to buy property.