I wouldn't support nerfing rogues, and haven't heard many complaints that they need one relative to other classes, and especially with their 11th level ability.
That's fine.
Obviously this isn't a big deal to many people, but to address your questions:
How does disadvantage keep a fighter from getting 3 attacks/turn? It hinders their chance of success in each of those three attacks.
What affect does disadvantage have on the druid's ability to become an air elemental? None unless the druid is attempting an attack roll or skill check or save where that disadvantage would apply.
What impact does it have on the Heal spell, or Globe of Invulnerability? None, but how often can a caster use those spells in relation to how often a rogue can use RT? Once or twice versus several (dozens perhaps).
Or the Conjuration wizard's 10th level ability that doesn't allow damage to break concentration on conjure spells? Well, if the check was made with disadvantage, a DM could rule the PC still had to make a check, but allowing one of the two dice to "auto-succeed". So, you
could apply it here (and likely we would... we want to be fair to the rogue after all.

).
In the grand scheme of things, let the skill monkey be the God of skills at high levels.
Expertise alone accomplishes this. RT makes it overkill for those skills. We just reached tier 4 and our rogues are +17 and +16 to Stealth. With RT, they are pretty much undetectable when they get to Hide (often considering one has a Ring of Invisibility and the other is a Wizard with Invisibility prepared all the time).
They can't chain lightning, or wall of force, or roll a 20 to hit and THEN burn 8d8 divine smite attacks.
True, but those other classes don't get Expertise, Cunning Action, Uncanny Dodge, or any of the other at will abilities of a rogue. And as for the 20 to hit, see my other thread about playing with critcal hits:
Just curious if any groups out there play without the natural 20 is a critical hit mechanic? I know certain features would have to be altered, such as Champion fighters. Anyone? (listening intently in the echoing silence...) EDIT: Just to be clear this is simply a discussion, I am not...
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