Sorry, but are you now bringing in (quite high level) spells into this?
And counting repellant blast as an auto-kill doesn't get us anywhere, I'm afraid. Sure its useful in that particular scenario, but going to the lengths where you say you'd rather have repellant blast for the off-chance of doing that over reliable damage?!
As for Sorlocks in general, the comparison can't ever become fair unless you consider the character's defense. After all, the basic attraction of the Crossbow Expert is that she is a fully fledged fighter, with all the sturdiness that comes with that chassi.
I think we will never get anywhere if we don't try to focus on a single case - a player desiring to create a character focussed on dealing damage through weapons. What options are there?
One more thing: I'm sure this isn't the first time where I ask y'all to not merely calculate -5/+10 as 25% less accuracy. That's exactly the simplistic analysis that probably made the WotC designer think the feat was alright in the first place.
Still, you say something I would like you to expand upon. You say SS "isn't responsible for ranged dominance in 5E". You mean there is something else that carries that responsibility? And I think you say you need -5/+10 to make fighters fun. Do you mean that fighters aren't fun in a game without feats, or what?
To me it's obvious -5/+10 must be taken away from archers in particular (because otherwise ranged is equal to melee and therefore superior) and fighters in general (because otherwise every other fighter build is left in the dust, and monster HP melt away far too quickly).
I'm repeating this, because I feel uncertain where you're going with the discussion, and wanted to ensure we're still talking about the same thing.
Oh, come on! If we're talking about 12th level Sharpshooter Crossbow Experts, there's nothing weird or "quite high level" about 4th level Wall of Fire (available at 7th)! (Especially considering that Spike Growth works just as well starting at only
3rd level--although that requires cooperation from a druid, ranger, or lore bard, which I think would start another argument over party cooperation/composition.)
Repelling Blast is quite good in a number of different scenarios--you can't claim that it's being taken only for the specific scenario of knocking enemies off cliffs. It has damage and control applications. Besides, all you asked for was an example of something better than Crossbow Expert/Sharpshooter.
Sorlocks aren't at all fragile. Sorcerer 1/Life Cleric 1/Warlock 2/Sorcerer 8 gives you AC 20 (up to 27 if needed with Shield of Faith + Shield spell) plus 57 spell points (or equivalent spell slots) plus 2 first-level warlock slots (or 4 spell points). Put that together with the intrinsic defensive advantages of ranged combat and you have a PC who isn't fragile in the slightest.
You are trying to limit the discussion to "a single case", but doing so is leading you to false conclusions, like believing that ranged superiority is predicated on Sharpshooter's -5/+10 bonus option. You could disprove your hypotheses with a little effort if you were willing to look at the broader cases, like Sorlocks, but because you've limited yourself to that single case it apparently doesn't occur to you to examine related cases.
Fighters aren't fun (IMO) in a game without feats, because feats are so much a part of their identity. E.g. the Champion with a Healer feat, or the knight with the Heavy Armor Master feat. I think fighters could still potentially be fun in a game where feats can't be taken with normal 4th/8th/12th/16th/19th level ASIs, but if you bar fighters from taking feats with their bonus 6th/14th level ASIs I think they become boring--like a sorcerer who's only allowed to spend sorcery points on extra spells and not metamagics.
I think Sharpshooter and GWM are important for fighters' fun because that's how 20th level fighters can claim the title of "best at-will damage dealer in the game", which gives them a niche. If you were interested purely in tanking you'd be a paladin or paladorc instead. If you eliminate Sharpshooter/GWM then the title of "best at-will damage dealer in the game" goes to someone else like an Eldritch Knight 7/Warlock 2/Rogue 11, which I find a bit silly.
In short--and I don't want to be disrespectful here so I'll try to put this gently--but I think you aren't yet seeing what's actually happening with the 5E game rules, and you're jumping to conclusions about how to "fix" the discrepancy you do see. You admitted yourself that you didn't perceive ranged superiority until a few months ago; I perceived it years ago and I've had a lot of time to see factors which make it even stronger, and ways to exploit it more efficiently.
The source of ranged combat's superiority to melee specialization in 5E is a confluence of factors including (1) very flexible movement rules including mounted combat rules; (2) elimination of "requires +2 or better to hit" and introduction of at-will cantrips/elimination of old-style Magic Resistance, which removes one of the main factors that used to make melee combat necessary; (3) introduction of richer and more effective defensive maneuvers, especially Dodge; (4) harsh range limits on monsters' abilities like Medusa gaze which rewards not getting into melee; (5) bounded accuracy and strong summoning spells which makes it both simple and effective to flood the enemy with weak meat shields--without this it would be viable for an enemy to simply ignore a ranger's or sorlock's meatshields and go after their master, but under 5E rules the meat shields and ranged attacks synergize in a way that melee attacks do not, especially given concentration rules; (6) light/obscurement rules which make it possible to gain advantage at range as easily as (but differently than) when in melee; (7) feats like Sharpshooter and Spell Sniper which synergize with Dodging rules to allow e.g. one tank to hold a chokepoint while all the ranged PCs behind him slaughter the enemy with ranged attacks without a penalty; (8) cheap equipment, cantrips (mold earth), and tactics for impairing enemy mobility; (9) fighting styles (Archery) which synergize better with Sharpshooter feat than melee styles (Dueling, Defense, Great Weapon Fighting) synergize with melee feats (GWM, Shield Master, Polearm Master).
That's all I can think of off the top of my head. Only a few of the factors are even tangentially related to feats, and the -5/+10 aspect of Sharpshooter really doesn't even factor in at all.