How do actual ratings used in guides help this, exactly? You say the ratings let you know the relative power level/usefulness of abilities in relation to other classes, but I don't think this happens in practice. Let's use your example of Aura of Protection and see what we can tell from the first two guides linked to in the sticky.
The first guide by Gladius Legis ranks it Sky Blue (2nd to best rating). This is the same as Martial Weapon Proficiency, Divine Health, Lay On Hands, Divine Smite, Spellcasting and Extra Attack (among others) in the guide, so it doesn't stand out as especially good. The same author has guides for Fighter, Ranger, and Rogue. His fighter guide ranks Martial Weapon Proficiency, Action Surge, ASI, Battlemaster, and Eldritch Knight Spellcasting as sky blue, while his rogue guide ranks Expertise, Thief's Tools, Sneak Attack, Evasion, Reliable action, and Arcane Trickster Spellcasting the same.
Are all of these abilities roughly equal in game-changingness? The ranking he gives Expertise and Martial Weapon Proficiency is exactly the same as he does for Aura of Protection, so the ratings don't actually help reach your conclusion of which one is a big change. Is Arcane Trickster and Eldritch Knight Spellcasting as good as Paladin spellcasting? They are all ranked the same, and all are ranked the same as Aura of Protection. Is immunity to disease really on the same tier of ability as Aura of Protection or 1/2 or 1/3 Spellcasting?
The next one by Evil Anagram is similar, although sky blue is it's top rating. It ranks Martial Weapons, Aura of Protection, Divine Smite, and Improved Dive Smite as sky blue, but ranks spell casting, divine health, and extra attack lower. Protection is standing out a little more in this list, as he's ranking fewer base abilities at the top. So lets look at some of his other guides. For the Warlock, only Pact of the Chain and "Awesome Cantrips" rank sky blue, their entire pact magic casting ability and the ability to use invocations ranks lower than Aura of Protection or Martial Weapon Proficiency. Sorcerers have both Spellcasting and Metamagic as sky blue, while Bards have Skills, Spellcasting, Bardic Inspiration, Jack of All Trades, and Magical Secrets with that rank, and fighters get ASI, Action Surge, Extra Attack, Martial weapon proficiency, and archery fighting style. Does having these abilities ranked the same convey significant information to you? Because it doesn't to me.
Note that I'm not saying any of the guides are bad, just that I don't think that their ranking of individual abilities actually conveys much useful information. And specifically, that the ranking doesn't convey the information 'this is a major game-changing ability, while this one isn't' that you think it does.