I appreciate the long reply, but some things here I feel aren't correct.
Firstly, I think the idea of a "true tank" is a bit redundant, because even Ornn can build super tanky, be as tanky or even more so than Nautilus, Zac or Maokai and do tons of damage, that's just balance wise that these things should be fixed. Anyone can pretty much be a tank as long as they have the necessary base stats (HP, armor and mr) with relative ease so the idea of making Malphite a true tank doesn't really make sense, since the only way tanks do damage anyways is by comparison. They one shot an adc, but an adc can't one shot them back. And that applies to any tank pretty much.
I agree that Malphite gets destroyed by AP, that's part of his gimmick. But making something incredibly unfair to one role and saying it'll be ok because he gets destroyed by another is a toxic concept that could make games unfun because of the lack of counter play born from something as simple as picks choices. Basically, you lose the game from match select, or you don't. This idea shouldn't exist. The game should be all about outplays and how to outsmart your opponent. It's more fun that way and more challenging skill wise. When you have a champion like Malphite that walks around and just tanks 5 billion damage due to the innate armor he builds anyways for his gimmicky playstyle and on top of that gets a shield that makes attacking him even more tedious, forget about it.
Tl;dr : he can be counterpicked, but counter picking shouldn't be how games are won, it should be with actual skill.
Note : his laning phase against auto attacking champions would also pretty much be an auto lose, which is toxic design.
On the third point you made, I appreciate the mind games he's able to pull off in this kit, but that doesn't make him any more fun. It's still as tedious and feels a bit like Sion, except without the actual skill of landing his ult or Q. The whole point of the rework I thought of was to put more skill input possibilities from the player with skill shot and reaction based abilities, that would also change up his playstyle from walk into the enemy team and ult into E combo, to a playstyle with more intuition on whether or not to use his E, or his Q, when to protect allies with his W, or when push comes to shove, use his ult to push back enemies. Every ability being a skill shot in a way except for his W. This would for sure make him more interesting to play with than the basic Vanguard playstyle.
And as for the Rammus comparison again, it doesn't matter who copied who first or who did what first. This isn't a time based competition. The only truth here is that Rammus is currently more effective than Malphite and more fun, being able to do the exact thing Malphite does without the attack speed slow and with a better cc for adc's, a taunt, which is countered by QSS. The description you gave Malphite is ironically the description you can give to ANY tank you listed, which proves my exact point, he's a very basic adc counter gimmick; a downgraded version of Rammus. I'll even quote you : "Want to be a zoning cc monster who can peel or engage? Be Malphite.". Guess who else can do that, literally every tank, the zoning aspect isn't even a Malphite thing, ANY tank can zone due to their tankiness just by standing in front of an enemy, and even Ornn, the "damage" tank as you called him, is played support now because of his cc. So he can peel and engage too.
Tl;dr : Malphite currently has a niche, yes, but it's been done better by Rammus, and is due for a rework that should change everything hopefully, otherwise he'll still be the boring mess he is now.
I'll finish with something you said : "He should instead help is team survive/fight, and help them win.". This sentence here goes against your whole rework idea because with the playstyle he currently has and the playstyle he will have with this rework which is an enhanced version of his previous self, the only thing he will do is be an R bot. Press R on enemy and use abilities in most likely the most time efficient way possible, which is annoying to play/play against, since the gameplay has no depth.
Check the link if you're interested in a version of Malphite that helps his team survive/fight, as I think I've thought of a good way to do it by changing up his abilities but keeping his core feel of an immovable rock.
