But every new characte gets 2x exp as well
The Problem here is not that the new or old chars dont get double but that the retired doesn't...
There are three separate things about exp.
1) Retiring.
You retire, your exp gets reset, you get +3% bonus exp. So if you retire once, your tick at x1 will bring you 1030 exp instead of 1000. It is capped once you have retired 15 times, in which case you will get 1450 exp per tick at x1 (and 7250 at x5 accordingly). This bonus, as Harald said, is only applied to the character you retired.
2) Minimum x2 multi for characters below level 25.
This applies to any character no matter what generation. Instead of starting with x1 multi, you get x2 as the minimum. So if you had x5 and lost the round, you are back to x2.
Note, however, that the multi you have is
only shown correctly after the first tick (the first time you get exp in a round). S
So if you join the game with generation 2, level 10 character, it will show you your multi as x1, but with the first tick you will get 2060 exp and your multi will appear as x2.
3) All the exp you get (except on DTV mode I think?) is
doubled on the website, so if in the game it says you got 2060 exp, in reality you get 4120. This is not shown in the game in any way, only on the website but it effectively means you get twice as much exp.