Healing has already been noted as an issue and I want to bring forth how to deal with it and all the advantages that could come with it.
This is more of an idea, rather than a direct suggestion or feedback to something specific. It's more of a view of how games like these feel to the player and how to bring forth an easily controlled game setting.
Healing has been noted in this game as an issue, where fights easily become monotone in endgame. Lots of healing from passive healing to different abilities makes sustained close range fights easy to manage and makes the experience dull to the player. This is commonly counteracted by the most straight-forward idea of increasing the difficulty, but this brings forth some other issues that are commonly overlooked. Increasing the difficulty in such a setting often implies harder hitting enemies and more erratic patterns and movements. This can often be seen implemented as shotguns, jumping enemies and cluttering bosses with lots of minions. It is one of the only ways to deal with the issue, since a players HP has to go down faster than they can heal in a fight. This creates some more issues, though.
Dying within a couple of frames always feels unfair. Getting instantly popped by a shotgun or getting jumped on and dying within a couple frames feels unfair. It is the mistake of a single action that could make you lose many many hours of progress within the blink of an eye. It also creates a significantly harder time increasing the difficulty more. There is not many options in terms of increasing the difficulty beyond those mechanics. The more the difficulty is increased, the less skill based it will feel as the difficulty only increased quick-killed chances. It only results in the least interaction possible being the safest approach. This creates more incentive to leech or just not participate whatsoever. Fights will still feel dull between the moments of imminent danger and the mistakes you make are more devastating.