I find a magnifying glass and an aluminium straight edge help a lot in evaluating the teeth before, during and after sharpening. My saws were all old ones, so they had seen some wear and some sharpening before I got hold of them. Some teeth were higher than others, some gullets deeper than others. But the majority of my usage is about 3 – 5 cm of contact with the wood, so a bit of a curve is not too much of an issue. A longer contact area may make the curve more of an issue, and it may be this that makes you think some teeth are not cutting as well as others.
It would be worth checking if the tips of all the teeth are at the same level, just so you have a better understanding of the state of the saw before you start filing them all down.