Overall a solid build. However, dust is the big culprit there, but the other factor is the front of the case. Appreciating that I only have your pictures to go by, the front looks terrible for intaking air. Those holes are so small plus air has to make a 90 degree turn before it gets drawn by the fans into your case. It's the equivalent of trying to breathe through your nose while one of your nostrils is stuffy - sure it'll work, but it could be better.

Regularly cleaning your PC when it gets dusty will fix a lot of problems with airflow. For now, your AIO is doing a great job keeping the CPU cool.

If temperature eventually does become a problem, the next step is to swap your case out with something that has much less restrictions on the front. There's lots of cases out there to pick from, but a solid popular one is the Corsair 4000D, to give you a reference point of what to look for.

EDIT:

Just saw you also mentioned your thoughts on upgrading your fans that I thought I'd respond to. I think you're fine for now if you just clean your PC and make sure that air can get through those holes. If you notice temperatures get really bad to the more critical components, I recommend case swap to introduce more airflow. Your money's better spent there.