You don't need 12 hours every 2 years to keep your license vaild. That keeps your SEP rating valid by experence.
For the OP if you think of things in two streams.
You have the license side of things which govens in what capacity you can operate ie can you earn money doing it or not and fly as a Captain of a multicrewed aircraft.
And you have ratings which each have there own time valid for and method of renewing/revalidating.
As for whats safe for one might not be safe for another on the currency side of things. There are some that can go a year without flying and you would never know sitting next to them and there are others there is a marked drop in competency after only 2 weeks.