That is also true. The weight takes the position into account by comparing the bets of the players, which in case of a take over are (relative strength at takeover)* potSize / 2.
The current formula for the applied weight to the rating change in direct comparison between two players is
1 - | player1.bet - player2.bet | / max({player1.bet, player2.bet})
with |.| being the absolute value.
This means, that if you take over a weak position and lose, you won't lose that much of your rating due to the low bet you had to pay. You will also not win that much, if you can win a game after taking over a strong position as your bet will be higher than that of your opponents.
However, you will also win less than original members of the game, if you can achieve a victory with an initially weak position or you will lose less, if you fail with a strong position. This is in accord with your observation, that players taking over win or lose less in any case.
The best gains currently can actually be made if you take over a position with equal bet as other members, so a position that is twice as strong as any other. In this case the weight will be approximately one. I believe, the rating weight was introduced when takeovers still costed full prize. I cannot say, if leading a weak position to victory or failing a strong position being less rated was originally intended.