In a game about fighting, you'd think there would be at least one subclass for the player who wants to play the true glass cannon - with truly stellar DPR to compensate for being such a fragile frontliner character.
Except the rogue isn't that fragile. They aren't the biggest cannon, but they aren't particularly glass either.
The crucial point is a lack of a feat to correspond to the fighter's -5/+10 feats.
In particular it's their inability to combine the +10 from sharpshooter with multiple attacks with some sort of mechanism to mitigate the -5. They can hide for advantage on one attack and hit decently often, especially if they have elven accuracy, but they're not in the same league as a battlemaster with action surge and precision attack.
Why not make it relatively simple to get your two sneaks per combat round? That's the approach of almost everything else in 5E.
If you give them a way to reliably get a second sneak attack every round, then they do end up outclassing fighters. It's really only certain fighter builds with the right subclass and feats that consistently out-DPR the rogue with one sneak attack.
As a baseline, with no feats at levels 5, 11 and 20 (when the fighter gets another attack) and assuming matched to-hit, the greatsword fighter is doing 22, 36, and 48 damage times to-hit per turn (not factoring in action surge or GWF style, nor crits) whereas the rapier rogue is doing 19, 29.5, and 43.5 times to-hit. But give the rogue booming blade, and that goes up to 23.5, 38.5, and 61.5 (more if they can induce movement).
Now add in action surge and a couple of feats. Assume a 60% base chance to hit if you take ASIs at 4 and 8, give the fighter PAM and GWM at 1 and 4, and give the rogue magic initiate (wizard) for a familiar (or just be an AT) and elven accuracy at 4 and 8. Then assume 7 combat turns per short rest, so the fighter is doubling their damage every 7 rounds, for a DPR multiplier of 1.14, and assume the rogue gets advantage 3/4 of the time.
Now the fighter does
28.5 x 0.55 x 1.14 = 17.9 at level 5
79 x 0.35 x 1.14 = 31.6 at level 11
99.5 x 0.35 x 1.14 = 39.8 at level 20.
The rogue does
22.5 x (3/4 * 0.80 + 1/4 * 0.55) = 16.6 at level 5
39.5 x (3/4 * 0.94 + 1/4 * 0.60) = 32.0 at level 11
58 x (3/4 * 0.94 + 1/4 * 0.60) = 47.7 at level 20.
That's biased a bit in both directions, against the rogue because we didn't factor in crits and we assumed that targets hit by booming blade never moved, and against the fighter because we assumed they never had advantage and didn't factor in GWF style, but it's probably close enough to demonstrate that in terms of melee DPR, even with feats, the base class rogue is competitive with the base class fighter for on-turn damage. It's a different story when it comes to the Battlemaster, since precision attack can make a surprisingly huge difference when coupled with -5/+10 feats. And it's worse for the rogue at range, between the impact of archery style for the fighter and the relatively poor value proposition of SS for a rogue (on top of the loss of booming blade). But the point is that if you wanted to boost the rogue's damage output to match the fighter, it'd be about giving them some more subclass/feat options they can take in conjunction with existing mechanisms to aggressively optimize for damage, not about boosting the base class.