Tensei Kenja no Isekai Life ~Daini no Shokugyou wo Ete, Sekai Saikyou ni Narimashita~ - Ch. 68.2

[Aricitic]

He could tell the magic went past it. So either he just missed, or it went through without effect. If he can't sense it being used up, then he logically can't sense it going past either. He had to know enough about the spell's strength to detect it going past.

You could certainly be correct. I (hope that I) have never claimed to always be absolutely correct all the time.
My interpretation of what was shown is that his "dispell" has a visual element to it and he was able to see roughly what we could see from "slibird."
Edit (reread your post, clarification): if he is going based on vision alone (shared vision with "Slibird") then from his/their perspective it would have appeared to pass through. Because it remained there, based on vision, it would "appear" that it had "no effect". If it's based on vision, then if, say, 1% (or less) of the curse disappeared from the area the dispell passed through, he could, visually, miss it. Curse or otherwise it was clearly very, highly condensed before it started spreading.
That could, very easily, be purely an assumption on my behalf, but I am going based on what was drawn and said.

Additionally, the fact that is later able to affect it suggests that there was an effect similar to my fire/water metaphor.
Additionally, the fact that he needs one of his tamed creature's eyes to visually see if the "smoke" could pass through his barrier(s) suggests that he's not going by a reaction to the magic. This and that are different things, so, as always, I could easily be wrong.

Another Edit: I feel that I should try and make abundantly clear that I am not trying to make "the case" that you are (completely or otherwise) "clearly wrong." I can't make that case. I don't have the right to make that case. I am, however, explaining how I interpreted what I read/saw.
If, for example, you have read the source material, or any additional material that I have not (and I have not so that wouldn't be hard...) and that material says more than the manga on this, then my interpretation of the events is clearly incorrect.
The only thing I can have any accuracy on is what is quotable from the manga... and with regards to that the only thing you didn't get accurate (I won't even use "correct" here) is the few lines on the page (or page after) it shows the magic passing through the curse. Even these lines are open to interpretation, and I could have misinterpreted it.

 

[glscarves]

Remember people, we could have avoided all this destruction and disaster if Yuuji just instantly yeeted it while it was mid-process with the bad guys, instead of being cuck mc who doesn't want to reveal his powers and just watch instead of doing nothing.

Imagine like you see an electrical outlet sparking with flammable materials nearby. You would immediately do something about it.

Yuuji is the guy who be like...

- Oh, it's sparking. It's fine.

- Oh, something caught on fire from the sparks. It's fine.

- Oh, it's now burning the furniture. It's fine.

- Oh, the room is on fire. It's fine.

- Oh, the house is on fire. This is fine.

- Oh, now the neighbourhood is in flames, millions of $ in property damage is done, it's approaching a nearby forest, people are being sent to the hospital.

Guess I better do something about it now.

 

[screamdoom]

I sense an explosion might coming

 

[chickenstalker]

Getting tired of this Academy™ arc. When will it be over?

 

[MCX01]

Someone else able to use absolute cleanse?

 

[breakthelimit]

Honestly still annoyed at how much the anime messed this book up. It's so clearly a satire and comedy, and they played it so straight.

Ah I get you..and the worst part for me was every time he uses spells it like watching a gifs.
well I like the slimes tho, they’ve done them right like in the manga.