Mercy has been meta for the last like 20 seasons.
S18+: Hanzo Widow meta → Mercy fit that meta well
S22+: Ashe meta → Mercy hard meta
S25+: Echo meta → Mercy hard meta
S28+: Soldier meta → Mercy good enabler
She is literally like Tracer, not a meta hero but fits EVERY comp and is like a very flexible, one-size-fits-all pick
etc.
Now Sojourn is meta (actually BUFFED with a Mercy). Not to mention tank rezing potential (I am fine with rezing DPS or supports, even obnoxiously hard to kill ones like Widow, but rezing a tank is definitely NOT OK). But please Mercymain cry about how your hero “hasn’t been useful in forever” when she has been meta like last 20 seasons.
no, that’s not what I’m saying, you should learn to read, I’m saying that damage boost changes breakpoints and makes a hero that would be healthy in a vacuum (with a TTK of 1.5s which is a very reasonable TTK) into a hero that will likely be obnoxious (with a TTK of 1s which if you factor in human reaction time of 0.2s leaves you with 0.8s to save your teammate).
Ashe
Widow
Echo
Phara
Hanzo
Soldier
McCree (the brief period he was meta)
now Sojourn
ALL nerfed because they were oppressive with a pocket bot. But sure the problem is that those heroes were oppressive! Totally not the fact that most of those heroes have a glass cannon design, and would be easy to kill without the egirl pocket bot making them immortal gods.
Would love to hear your take about how release Echo was OP when in SEITA arena (idk if Mercymains know this mode) Echo was like a top 7 hero at best, the best heroes to get in that mode being Baptiste (a SUPPORT HERO), Tracer and McCree.
Hanzo another hero that was extremely oppressive in s18-s20 (I know most don’t remember that “Hitscanzo” meta, is like a top 8 hero to get in SEITA, he loses most 1v1s vs heroes like Genji, Tracer, Bapt, probably even Soldier beats him most of the time.
Nanoboost is an ultimate I know that Mercy mains have a problem distinguishing ults and basic abilities since their E button has an ultimate attached to it, but playing vs Nano-boost every 1.5-2 min is nowhere as oppressive as playing vs a Sojourn/Phara etc. being PERMA pocketed for 80%+ of the game.
she ruined like 8+ DPS so far in the last 15+ seasons, making them average af without a pocket, try playing anything other than Mercy pls, try playing Ashe with an Ana Lucio in team and tell me how hard you carry when every 50 damage you take from a Genji doesn’t immediately get healed and as a result you have like 30% more downtime due to being forced to play cover.
have you ever tried playing Tracer? I’m a 3.8 Tracer from OW1, and after the latest buff she got, I thought I would destroy lobbies. I do have a positive winrate but healing is so strong (due to there being 1 less tank so supports can focus more on other support/DPS) that sustain heroes (Tracer Soldier etc.) are garbage. Tracer still survives just because she is a “constant force attention” hero, but the reason 1 shots are meta is literally because SUPPORTS HEAL TOO MUCH IN OW2 NOW THAT THERE IS 1 LESS TANK TO HEAL, they buffed tanks to accommodate for them taking more focus fire, they nerfed DPS due to less shields/tanks to mitigate, but they forgot to nerf supports 
Sojourn is a bit broken but without Mercy in the game she would only be slightly overtuned. Both heroes are a problem and Sojourn needs a slight further nerf but also 8+ DPS getting nerfed in OW1 due to Mercy synergy teach us that DAMAGE BOOST IS A PROBLEMATIC ABILITY.
Again if you think otherwise, please queue DPS on your equilibrium elo, ask your supports to go Ana + Lucio or Ana + Zen, pick Echo or Ashe and see how oppressive those heroes are without a Mercy.
FYI I played at near highest ranks in OW1, went vs T500 hitscan players very often, in OW1 the last 5-10 seasons 70% of the time you would go vs Ashe perma pocketed by Mercy, I don’t think there is less engaging gameplay to go against and it’s a shame because Ashe is such a well-designed character otherwise.
(fyi other than 1 shotting you more easily through healing with headshot-hipshot, or headshot-bodyshot while getting healed combos, Ashe was oppressive in OW1 also cuz thanks to damage boost you would get BOB literally every 40s, BOB in case people don’t know is the strongest DPS ult in the game next to old EMP maybe).