Whilst modern fighters have been labeled such as multirole, swingrole, air dominance, etc, each was developed to fulfill specific mission requirements of each developer country.
In the case of the USA and Russia, the F-15, and Su-27 series were developed as air superiority fighters to counter each other at top end of fighter spectrum, hence a higher degree air-to-air sophistication and cost.
At the lower end we have the F-16 and Mig-29, hence lower cost and greater numbers. These are primarily meant for closer in, battlefield support, hence emphasis on low altitude performance, and air-to-ground systems.
In simple terms, the high end F-15/Su-27 have specific mission requirements different than the low end F-16/Mig-29 which is why they co-exist and compliment each other.
So far, I've discussed the USA and Russia which developed these fighter. So what about the rest of the world? They are customer countries and will buy fighters "off the shelf" to fulfill their requirements too, but this gets often muddied because some countries have similar hi-low end requirements (Israel, India, Japan) and others do not.
Two fighters which must must be mentioned are the F-18 series and Rafale. Both are designed for CATOBAR operations which puts them a tad behind their land based counterparts in terms of performance. However, they do enjoy use by air forces for non-carrier operations.
IMHO the advances in fighter technologies have somewhat closed the gap between the high/low end capabilities, so comparisons can get rather confusing. I personally do not believe in fighter vs. fighter comparisons as there are multiple variables which must be taken into account, a tough task.
Bottom line is that aircraft are developed/chosen to meet mission requirements (and cost) for the end user.