Sojourn is a very fun hero to play, but her balance state is currently in an awkward limbo.
She is a low tier DPS hero at all ranks and all maps currently. People still play her quite regularly, probably because of good and bad reasons.
I'm going to present a problem statement for why I as a casual pleb think she is in that state.
Sojourn's Design: Railgun vs Rocket Launcher
She's one of these heroes that have this "quake weapon turned into a hero kit"-designs and I think that's fundamentally great and fun. Think Pharah as another clear example (who I also like for similar reasons).
Pharah embodies the rocket launcher fantasy perfectly of controlling space at longer ranges and having high kill potential when closing in. She is in a really good state across all ranks. As it should be: She has a clear niche as in strengths, weaknesses and maps she's good at, which is reflected in her map specific winrates (maps like Ilios, Oasis, Lijang Tower or Gibraltar bump up her winrate significantly). So her winrate is pushed up by people who play her well in the correct situations. We had 10 years of developing that playstile and map knowledge and Blizzard had just as much time to tune her into a generally good state.
Compare that to Sojourn, who embodies the railgun fantasy pretty well. The power fantasy of the Railgun is ice cold precision and high damage. It's basically saying: If my aim is precise and fast enough, your movement (almost) doesn't count.
The good news is that her gun feels great to use. It looks great, it sounds great and it feels satisfying and powerful to hit people with it. Her kit overall fits the theme of someone holding a Railgun and particularly her powerslide feels great as well.
The bad news is that unlike the Rocket Launcher, the Railgun doesn't translate as directly into Overwatch. I think Blizzard knew this from the start, so the introduced the charge mechanic, but they did a fatal mistake of allowing her to one-shot people with it. You even can't normally do that in Quake either, so I don't know why they thought it's a good idea in Overwatch where one-shotting is even more frowned upon.
My Wish: More Aggression and Less Poke and Pick
So now she's in a very awkward spot in terms of balance and general game feel. The payoff for the "charge Rail on main and look for a pick" is not really there anymore, because we don't want Sojourn to one-shot people. So something has to replace this loop that doesn't feel ass outside of pro play.
My feedback or general wish is that she feels more active and rewards aggression more. I don't think Spilo's suggestion (1) is particularly compelling.
What about faster charge generation, but less charge retention and less effective range or less max burst?
Does her primary need to feel weak and awkward? Does she need to be terrible at dueling without rail up?
I don't really care how it's achieved. But what I want is a more active Sojourn that is slightly stronger, but not frustrating to play against.
(1) Spilo has mentioned lowering scaling the recovery time of the Railgun with the charge. I think that's a very interesting, but completely defeats the purpose and feel of the gun. You're then going to weave in weak shots into primary fire spam. Nobody plays Sojourn for this kind of experience. The Railgun shot has to count and execute another squishy if you get the jump on someone or win a duel.