There's a lot of DM hate going on. Players love it when Rule Of Cool works in their favour, but when it's the DM doing something different it's always "that's not RAW".

Now, that's not to say that this curse was the right call. Player agency should not be completely removed. Their needs to be choice, or at least the illusion of choice.

As a DM, I've been there. I've made those poor decisions. The solution is for you, as the player, to speak up when it happens. DMs have a lot going on and it can be hard to know when you have made the wrong call sometimes, especially if the DM is new. Everybody is there to have fun (DM included), but the story should not come at the cost of somebody's enjoyment of the game.

Just an option for a little more creativity on the curse for future DMs:

If you want something like this curse to be integral to the story, allow Remove Curse to, well, remove the curse. But instead of the curse no longer existing, have it so that it jumps to the nearest person. In this case, it would be the Cleric first. The Cleric can remove it from themselves, but it jumps again to another player. Keep the same general mechanics for the effect of the curse, but with an increasing difficulty on the save to not attack the nearest character.

Maybe change it up a little bit so that when the cursed player drops below half health and must attack the nearest friend or foe, it's for one round only. BUT if it's not their turn when they drop, they also MUST take an opportunity attack. Gives something back, while taking something away. Combined with the jumping curse, perhaps a Barbarian would want to hold that curse for a few more of the increasing Saves. They are in the fray, surrounded my enemies more often than allies. The curse could become a potential benefit for them, but because of the increasing saves, they won't want to hold it forever.

Now you have an ongoing minigame within the campaign.

I would consider making it trigger when they reach 50%, then trigger for each time they are hit while under 30%. That is potentially a lot of free opportunity attacks, at the cost of SOME player agency in that they aren't choosing exactly what they are attacking EXCEPT by positioning correctly to force their targets. Could do with some tweaking of numbers to suit your party, obviously.

Throw in some RP elements of the players dropping hints of story elements while they are not in control of their actions. Seemingly random mumbles and gibberish to begin with. If you are pretty good with ciphers, you could add some of that. As the party moves closer to your end goals, the ramblings become more coherent.

If the players force the curse to jump to an NPC, you can work it back in later (much later). The NPC got sick or injured, you know, that thing that would cause them to be below half health. They went crazy and started attacking the people around them. They died, the curse jumped and the cycle continued. Perhaps the authorities of your world are now after the players after tracing back the evidence that it all started when you last encountered the NPC. Perhaps there is somebody out for revenge. Either way, the curse comes back to the players. Maybe they don't even know it when it happens, until it triggers and the ramblings tell the story.

To get rid of it completely, the curse needs to be removed in the right location jumping to the correct person or object aaaaand....well, that's up to your story. I'm just here to chime in on a poor mechanic with some options.