I don't understand why the difficulty slider doesn't also works on mini bosses for decreasing their stats. The mercury elemental really annoying. It feels for me that the developer overrates how much fun the fighting system is. Loosing fights over and over again, because you made a single mistake isn't much fun for me, if the whole fighting system is nothing more then switching convents and spamming healing items.
The Mercury Elemental should be a boss, everyone with that pentagram fight introduction. Minibosses don't have it, for example the Obsidian Shamans. Also, you immediately feel the difference between 50% and 100% boss difficulty, because it isn't just half the difficulty, it is more than that because stat reduction has a bigger impact. Pay attention that you readjust the difficulty slider again when you load a game, it resets (or it might just be on the first load after starting the game).
But besides that, I agree on the point that combat is too much about using healing items. Sure, you have the covenants and the abilities, but it also relies too much on using healing items. What was that comment again about not getting fat from eating all those flameberry pies? Just giving us more powerful healing items doesn't make it that much better.
Though in my opinion the action speed is much worse. One example is that you rarely have the chance to attack first if not already the case, switching tactics doesn't solve the problem (which I had at least hoped) and you might also want to have another covenant equipped at the beginning of the battle, especially since you don't get the first action. This is especially annoying if it is the case for the first enemy you encounter in a chapter. If you don't want to fight the enemy (for example because you want another one) and still get hit then your best option would be to just reload the game and get that lost hp back. The only alternative would be to stick with it and grind more.
To be honest, I had hoped the combat would take a different approach when I started this game but it quickly went into the direction of forcing more efficiency. Sure, there is some leeway, but mistakes are more severely punished, most often in form of loosing more hp items and which you could potentially run out of if you efficiency is not good enough. Someone would probably now reply about using the right resistances, but the point is that it is exactly what I mean, forcing efficiency, which should not be expected from every player.
I should probably mention that this is not just an average game, it is a porn game, so not everyone will take it as seriously as a normal game. Now you could argue about that people who are just interested in the scenes should just get the HD files or access to the gallery, but then they would be missing out on the story of the game, which gives these scenes some weight. Personally I think that scenes are much more enjoyable if you have context for them, a simple scene can't achieve that.
Back to the combat, there should be more leeway for mistakes in my opinion. The boss slider is already doing a good job for those who just want it to be easier, but that doesn't account for normal enemies and minibosses. You should also consider those who are more leisurely about this, not just those who are at least somewhat serious. With how the current combat system works, I am more inclined towards being leisurely and less about being serious.
This is not about how difficult the combat system is, someone who is more serious might have no problems with it, but how it is structured, which is why someone might not want to get serious in the first place.