Is it true that you get a better ranking while playing offensive characters than while playing support characters during placements?

I remember reading and hearing a lot of times that playing with a character who is supposed to deal a lot of damages and to get a lot of kills will get you an overall better personal ranking than if you just play as a support during the different ranked matches, even if you do a really good job, as you do way less damages and kills.

Since season 1, I have been playing the whole time with the same friend, who is playing support most of the time, while I usually take a DPS/tank position. So we were doing our placement matches together, and we did a good job most of the time. Though, after the placements during season 2 and 3, we figured that both times I ended up with 200 more points than him. So we have really been questioning if this fact was indeed true. He is mainly playing Zenyatta and Lucio, while I am mostly playing all the offensive/tank characters.

Taking two players who are as good as each other with one playing mostly offensive characters and the other support characters, is it really true that the support player will end up with less points than a DPS player? How are the different values of a match (kills, damages, healing...) influencing on those points?

Yes, at some point, Jeff Kaplan, the Game Director, has confirmed that Lucio and Mercy place lower than they should. Confirmed by this post. Ana and Zen do fine.

This was during Season 2. At the time of this answer, we are in the middle of Season 3 so I can only ASSUME they have adjusted it. The post claims Blizzard has fixes for them, but I cannot find the patch notes or posts by Blizzard confirming that have fixed it.