Which campaign? Russian jets vs NATO is always "hard mode" in DCS. (And in real life for the modelled time period, where NATO had fire and forget missiles and Russian missiles required constant lock for guidance. MiG-29C was the only exception.) I'd recommend "F-15C Georgian War" DLC campaign for its voice overs, fun missions and difficulty curve.
PS One can still win in the Russian jets, it just requires better tactics and skill. FOr example, DCS AI is not omniscient, you could sneak up to the F-16s from behind using Russian EOS optical targeting that does not trigger radar warnings.
Another approach would be to use the Su-27 massive fuel quantity advantage. Approach head on, bait the F-16 into launching their missiles, at 30 km separation turn 180 and run for a while to trash their missiles. Low alt with its dense air is best for this. Repeat 3 times and they will run out of missiles and be low on fuel. Engage them at your leisure. (This works even better against the slow F/A-18 as it can never catch up with the Su-27. F-16 is approximately equal speed wise.)
Also Russian missiles are faster than the amraams, and taking on a single f-16 is pretty easy, just by cranking/notching while keeping the lock and spamming the missiles (of which the Su27 has plenty). The F-16 will be too busy dodging. In close combat early F-16s are inferior to the Russian birds as the latter have off bore infrared missiles (R-73), so use them.
But the short answer to your problem is the "F-15C Georgian War" campaign