Scaling

Many areas of the game adjust your TIL, so that you are not too weak or too strong for the content. That will adjust your Damage and HP as if your TIL was at a specific value, which depends on the content you are running. But your main ratings will not change, your percentages will remain the same.

In this kind of content, contrarily to other places, TIL means nothing at all. The only thing that matters is your percentages, and Equip Bonuses. Removing items that give less than 15 stat points per item level means you will gain percentages. For now, that is mostly collars, guild boons, utility enchantments... And mount Combat Power...

For this kind of content, upgrading your items is almost pointless (it only moves a few stat points from most of your stats to one or a few of them, the sum of your percentages remain unchanged, just like Damage and HP). But there are a couple of things that matter, and that is what gives you bonuses to your percentages (campaign boons, the equip power of your companions, the equip power of your items...).

In order to improve some of your percentages, like Outgoing/Incoming Healing, or Forte, which do not have many sources in the game, it's preferable to reduce your TIL to the minimum. That is stupid, but that's because they didn't take into account the new stats when they reworked the items for the new stat system... So removing every item that does not give you any real bonus is the way to go in scaled content for healers.

Scaling certainly kills a big portion of progression. It's very badly implemented and makes no sense, because the system was rushed and not thought properly in the first place. Because items were not balanced properly and new stats were not taken into account. But, at least, newer players will be a bit useful in random queues. And players who build their character properly (even though they may be half naked) will still be way more effective than newer players.