Its true, but why this is boring? if you remove highground and you no need to deal with enemy on hg too, how it can be less boring? I assume that you will just attack from your starting position, why move or anything?
Again, we're not asking for all benefits of high ground to be removed, so range-dependent classes will still have an incentive to go to high ground. Just not a lob-sided "roll with Disadvantage or go to high ground"
In general if the player doesn't move they will be swarmed by enemies. Ranged casters have additional incentive to move because they're squishy. For example, wizard should have the opportunity to use scorching ray on a priority enemy without having disadvantage because combat started with an enemy ~3-4 meters away. Then they can move to safety. It's more fun to have player choice and it's more fun to have spell variety. Using magic should be as fun as playing fighter.
Also, having to always move to high ground slows down combat. The wizard in the prior example will always be in a sub-optimal position to deal damage if they're always chasing higher ground. So the player has to rely on guaranteed to hit spells like Magic Missile and Shatter to ignore disadvantage, while positioning the wizard where they need to be. (Being over-incentivized to use the same spells over and over isn't fun).
If the player doesn't use Magic Missile or Shatter and chases the high ground:
They have to move to high ground, now they're priority enemy may be out of range, now they have to start damaging another enemy that isn't a priority. (which slows down combat)
Person B) I disagree because "I just enjoy the game and I'm not sure why"
If its me, i guess i describe it correctly

I just don't get why "this make bless or other spells useless". You not always can be on hg, sometimes enemy on hg, so there many situations when this or other buff will help. And idk skills in dnd, but can assume that there some projectile with advantage or buff for allies. So they still will work for 90% of time too. And I don't feel that it lose to not be a Bless bot (or another strong buff with advantage), you just cast it when team really need it.
There are a lot of forum posts explaining why, it's worth it to take the time to read through other forum posts. If you're really curious about skills in D&D, there are plenty of online resources.
https://www.dndbeyond.com/spells