I listed healing spirit as broken as well. I houserule that the caster needs to use their reaction to trigger the healing. It’s an easy resolution to an incredibly poorly written spell. How did that wording make it past QA???
It uses the same wording as the other spells that operate this way. The difference is that this one heals rather than doing damage so creatures want to run through it.
I suspect the designers are in a ... modality ... that they care more about whether the majority of players are satisfied than whether the game is actually balanced or consistent.
I think it is more that they don't worry so much about rules abuse. When a player at the table took the spell I told her that we should do it 1/round rather than have it so every character can run through it like a sprinkler.
The whole table were surprised that anyone would suggest such a thing since it feels off.
Now, there are some balance problems in XGtE. Hexblade is the worst offender. It is both grossly overpowered and devoid of theme. That said, players who still want the theme of the Great Old One (or whatever) will still be picking that patron so it doesn't really matter. And while it is possible to make a Hexblade that is much better than other Warlocks and casters, most people won't be using it that way so it also doesn't matter. They will be using melee weapons and spending their invocations and spells on buffing their melee attacks.
The game is pretty darn resilient. There are only a few things which really swing things. GWM/SS come to mind there.
The other thing about balancing, is that most people are wrong. For example, most players of the game see the Wild Magic Sorcerer as underpowered, but really, it is much more powerful than the Draconic Sorcerer. Advantage on everything and the vast majority of the consequential effects are positive.
So how do they balance things? People are going to be upset about things. Designing to theme and story first is really the only way to do it. That's why something like Hexblade is so bad.
Personally I hope they decide to tell us a little about the data they receive from this, I would love to see the 'tier list' and the margins between them from a survey with this kind of reach. I wonder if this will lead to them finally settling on a solution for the ranger- is it a question of subclasses needing to be overhauled, or the base chassis, or what.
The problem with this sort of thing is that D&D is not a competitive game and most of its players don't have experience with competitive games.
Even in highly competitive games where the better options can be seen through people winning with them there is disagreement on tiers. In a non-competitive game like D&D options can never be actually tested.