Hmmh. I'm not very educated on Estonia but I believe you're also amongst the European countries with very low fertility rates. I'm not a big fan of US American ideas about society but you have a good point with the 401k. The tax exemption is a nice idea. And I also think the current workforce shouldn't pay for the current pensioners. It should be a fund and an investment.
By the way, the americans also pay like 10%-15% for their retirement if the internet is correct. So your 12% doesn't look far off if that's the entire number. But I'm likely missing something here.
And there's more. Demographics also weighs down on a healthcare system and maybe a few other things as well.