Death is about killing.
The dead are about the influence of those who exist in a new form of nature, including those who are the corpses of dust and the breaths of wind.
This may be a cultural difference, but no. That is not how that is generally perceived in my experience.
True Resurrection and Clone are examples of creating a new body. For example, if the original body exists but is irretrievable, then there would be two bodies (thus two ki lifeforce aura that cling to each body), but the disembodied mind (being the consciousness and self of the soul) unites with only one of them. There is no actual need to destroy the original body.
To remove a disease by pulling it out as ooze, or simply sweating it out or via urine or feces, is fine. Maybe for the sake of the story, yuckier imagery is more visceral and fun.
And both of those spells (True Resurrection and Clone) are listed as Necromancy spells. Additionally, we are talking about low level healing magic, such as cure wounds or lesser restoration, which do not create new bodies for the host spirit.
And, while it may make a good yuck story, that is not the visual presented with magical healing in DnD. We do have to be somewhat careful in not stepping too far outside the bounds of what DnD presents magical healing as.
Healing damage such as a missing limb has nothing to do with death or destruction.
How do you deal with the scar tissue? The bacteria in the air that latched onto the wound? How do you prevent the super cells that are regenerating at an accelerated rate from becoming cancerous? How did you get them to work in that manner in the first place (doing so requires destroying the limiters on cells)?
Yes, some of this is highly medically technical and may not be taking place, but it can easily fit in there.
Except when medicine doesnt work that way, such as by creating prosthetic limb or supplying a missing hormone, nutrient, or other chemical agent, or by supplying "good" bacteria for the healthy ecosystem of the gut.
Prosethetics aren't how healing magic works, that is something entirely different. But it is fair to say that supplying a missing chemical or healthy bacteria is a factor. But you must also remove the things that caused that imbalance in the first place. It does you no good to put good bacteria back in, if you can't remove the bad bacteria which devoured them all and caused the illness.
Killing bacteria and gaining assistance from undead souls ... are dissimilar concepts.
Neither are carnivores who eat meat the same thing as undead. Nor are Fighters who kill in combat the same thing as undead.
Necromancy is more specifically about dangerous magic, including undead, fiend, and the "Necronomicon".
That is only because you are artificially limiting it. This is similar to saying the only use for radioactive material is to create nuclear bombs. Yes, there is a dangerous thing here, but there are other uses. Also, nothing in necromancy as it pertains to DnD requires a fiendish connection. Every spell to contact or summon fiends is either divination or conjuration, not necromancy.