I know what you mean. Three seasons ago I carried myself out of Silver to Diamond playing mostly Soldier and Reaper. I stayed in high plat to low Diamond for three Seasons straight with more wins at the end of the season than losses.
This Season I started in Plat but ended up dropping to low Gold 2100 after about 30 losses. I had lost about 400+ SR a little at a time playing Soldier and Reaper.
I found that in every match other DPS would pick a DPS hero even though I had already locked into my main Soldier and Reaper knowing I could carry really hard, take down pharra/mercy with Soldier or destroy enemy tanks with Reaper.
I ended up losing over and over again if I stayed DPS cause there were three DPS and only one tank or one healer which was bad and we lose.
So after all those losses I had to start playing tanks or support and learn to carry as a tank or support and it worked. I gained back all the SR I had previously lost in half the matches.
I have about 20 more losses than wins but I was able to get back to Plat by hard carry with tanks and support. As tank (Rein or Orrisa) I had more elims, damage, and ult kills than the DPS on our team. As support I had more heals than the mercy or moira (I play Ana and Zen). I continued to win and gain 30 - 40 SR per win and if I lost a match I lost less than 17 SR.
I had several matches where as Rein I had 54+ elims, 17 kill streak, 20+ earth-shatter stuns with 17 earth-shaker kills, 14+ fire-strike kills (even pharrah), and 17+ charge pin kills with highest elims, highest damage, highest obj kills, and blocked over 20,000 damage. Its a hard carry when you as Rein have more elims, damage, and ULT kills than the 2 DPS combined.
So you can carry using other heroes and do not need to always be DPS.
However, there were matches where I was getting destroyed as tank by Pharrah/Mercy and the DPS was not dealing with it and I was just getting killed over and over again because our support was being destroyed by pharrah flanks. I told them I main Soldier and will kill pharrah and mercy if they let me play Soldier. Sometimes they let me switch to Soldier and sometimes they don’t. When they do we win cause I can kill pharrah and mercy with 47% accuracy and thus keep our support from being killed by pharrah.
With our support not being killed by enemy DPS such as Pharrah then the whole team can get sustain heals including the tanks.