I think you should be better off.

I did a small installation at my parents house with two panels at south-southwest-orientation with a 600 W inverter for around 800 Euro.

Turns out those two panels have created over 1.1 MWh since the late summer of 2023. With cost dropping heavily, your ROI should be much sooner.

The other aspect of this is the reduction of demand on the grid - which potentially reduces infrastructure costs ( or reduces the rise ) and hence shows up in a reduction in electricity prices ( if not absolute, against where they would be ).

A building sized thing has much higher installation costs. And you can't DIY it, it's not just plug and play.

That is true and it is where the regulation and bureaucracy comes in. I vouch for making building installations low friction and better subsidized.

Security will make this never as simple as balcony plug and play but there is a lot of room for improvement.