Which frankly is just laziness I think. It also seems to be an area where any reasonable DM will say "yes, you can treat disease with a healer's kit". Otherwise the way to totally screw your enemies is to infect them with a mundane disease, not to curse them (simply removed by any spellcaster).
Can
you treat disease with a first aid kit? Bandages, gauze, pain killers, tape and the like? What in the kit works against disease? Okay, disinfectant prevents infection from a wound, but it's not going to do squat against something you've ingested or come into contact with through the air.
Looking at what the kit says in the Basic Rules:
Healer’s Kit. This kit is a leather pouch containing bandages, salves, and splints. The kit has ten uses. As an action, you can expend one use of the kit to stabilize a creature that has 0 hit points, without needing to make a Wisdom (Medicine) check.
It's stretching to say that would be able to treat disease or remove a physical condition. It had one use: stabilize the dying. Anything else is a house rule.
Like I already pointed out - being blind or poisoned just applies disadvantage. You can ALREADY overcome it with aid another. Having someone give an improved aid another is not unreasonable, and the trope of the blind guy fighting while his buddy calls out "3 oclock! One oclock!" is fairly common.
That's Hollywood realism. Not everyone wants their game to be a Schwarzenegger movie. (And even then, the blind guy in combat is usually played for laughs.) And it really only works for a melee character. Range characters would be ineffectual.
Still, that's only a way to negate the penalty at the cost of your entire action. There's still no way to actually remove it. The warlord has to spent their entire turn every turn keeping an allying fighting remotely normally. Oh, and the character still
automatically fails any ability check related to sight. So that sucks.
Mitigation of max hitpoint reduction is already partly achieved through temporary hitpoints, as long as you can get them regularly enough. I already pointed out that revivify is basically already possible in our world, let alone with a world where a man can face off with his pointy stick against a fire breathing flying elephant.
Bringing people back from near death is more Hollywood realism that still doesn't translate well. Just because you have dragons doesn't mean all the rules of reality and physics go out the window. It's not a "get out of logic free" card. The magic is cool and interesting because it's the exception to reality.
A theoretical warlord might have an ability that let them bring someone back who was dead for a few rounds, but any longer and that steps on paladin toes (and creates a free version of a spell that costs 300gp).
But, really, if the warlord can get to the character that quickly, why weren't they healing them earlier? That's the problem. People die when you have a healer because they're out of healing, the healer was out of commission, or something like a coup de grace or massive damage happened.
Same goes for ability damage - inspiration. Parasites are a mundane threat, treatable by a healers kit. Remove curse is another "basically any spellcaster can do this".
If you have an entire party with zero spellcasting, magic will be an issue. Like if you have any entire party in full plate, stealth (and deep water) will be an issue.
Except that curing most of the condition list is now limited to clerics, druids and bards because someone just didn't think it through.
Let's see, in 3rd Edition
remove paralysis and
remove blindness/deafness were cleric/ paladin spells,
remove disease was cleric/druid/ranger,
remove fear was cleric/bard, and
neutralize poison was bard/cleric/druid/ranger/paladin. Only
remove curse had different classes, being bard/cleric/paladin/sorcerer/wizard. Oh, and
stone to flesh was a wizard/sorcerer spell.
Really, the *only* class with everything was the cleric.
5e made it so the bard, druid, cleric, paladin, and ranger can all remove some of those effects, and the druid, bard, and cleric can all equally remove them all. It tripled the classes that can cure most of the condition list. And made it so the bard - who only knows a few spells - might be an effective healer through one spell selection rather than 5+. And it made removing petrification easier, by having that spell available to people who actually remove conditions rather than trying to foist it onto the wizard/sorcerer. (Has any sorcerer ever wanted to take
stone to flesh?) But, since it's easy to add new spells, it'd be easy to have a wizard
stone to flesh spell that focuses on the utility aspects but just coincidentally restores petrified creatures.
So big improvement for 5e over past editions by making three classes equally adept at filling the healer role, and allowing two others to do half the removal and be adequate back-up healers. I don't see it being necessary to include the
restoration or
cure wound spells on the wizard and sorcerer spell lists.
But, again, the catch is that any class designed to fill the roll of the bard/druid/cleric should have access to those spells or comparable abilities. Otherwise they cannot fully do their role. It's like making a tank with d6 hit points; yeah, you might have the high AC but you can't stand up to many attacks. Relying on other classes to use those spells doesn't work, since that means the class isn't filling its role. That's like the fighter relying on the rogue for some damage mitigation or the evoker wizard requiring the ranger to keep their damage high.
Especially since, half the classes in the game don't get the spells. If you're a party with a warlord and three other characters pulled from the list of barbarian, fighter, monk, rogue, wizard, sorcerer, warlock (or even a bard that doesn't take those spells) and someone gets diseased or blinded then the warlord isn't going to be able to help. They have to stop adventuring and go find a temple or roll up a new character.
I don't mean "oh, I just failed my save, better get a reroll, oh, failed that too, guess I'm a rock", I mean "hey, bob failed his save and spent the rest of the fight petrified, lets give him another one. And another. And another", which seems a bit too good if anything. Eh, hard to come up with a great new mechanic in a few seconds.
A new save would be good. But it's super easy to fail a save even with advantage. And that'd be a great warlord power. But it's not going to
But if we're accepting a warlord that's not quite a full healer - if we have to accept one that is "close enough" but cannot do everything - that can also apply to things like not easily getting unconscious creatures back in the fight. Or using temporary hit points instead of restoring health. Because they're not replacements for a cleric/druid/bard but their own class entirely, in the same way a warlock can kinda replace a wizard but not in every way and a ranger or bard can kinda replace a rogue but not in every way. We can worry less about fitting some arbitrary "role" that doesn't *really* exist as a design space in the game and focus on making a warlord that is really good at doing warlordy things rather than a warlord that is really good at doing clerical things.