Galazie,
I'm not a particular fan of 7x50s but I have tried the Meostar 10x50, the SLC 7x56 and most of the 7x42s at different times. I can't say I noticed any deficiency in on-axis resolution in the more expensive ones, but I wouldn't expect to with a 7x models. The would be a difference in colour rendition, but how much would depend on when the Meostar in particular was made (the first two digits of the serial number). A different colour balance can alter colour contrast and perceived sharpness in different light conditions.
Henry is right of course. In principle, depth of field is dependant on just magnification, but there are conditions attached. It only applies to single points in the field of view (usually the centre).not comparing centre with edge. Just as the dof of a camera varies with aperture, a binocular dof varies with the diameter of the pupil of your eye. A cloud passing over will change the apparent dof.
You are right that a very bad binocular can alter the dof. The Meostar isn't a bad binocular. In fact the effective resolution of the 12x50 HD I tested was really exceptionally good. Your sample could have been damaged, in which case Henry's star test should help diagnose the problem.
Optical engineers come up with quite a lot of variation in field curvature and edge aberrations (like astigmatism), in the models you mention. There is consequences for the size of the apparent sweetspot and depth perception, but the differences generally mean they suit one field situation better than another. I'm sure you have a preference, but whether it is better or not is a different argument.
Using distant targets, particularly in a city, adds the complication of haze and the binocular transmission spectrum of course. I often find the models that are better at cutting through the haze, do not have the colour fidelity I prefer for birdwatching. I'm afraid I don't remember enough detail about the Meostar 7x50 I tried to comment, but the 12x50 HD I reviewed was very good on colour fidelity.
David