DOMSDOMS has nothing to do with gains.
Some exercises, like barbell good mornings, will wreck your hamstrings with DOMS, but that is because it's a lengthening (eccentric) movement, which is where DOMS shows up the most.
Concentric (shortening) and isometric (held motionless under tension) are not commonly DOMS inducing, and are primarily how abdominals are used. Your abs are braced tight (isometrically) during the deadlift, and contract (concentrically) during sit ups and squats.
If you wanted to cause DOMS in your abs, you can do something like an ab wheel, and rollout very slowly with your abs under tension, causing eccentric behavior.
But trust me (and every other human who trains) on this one: if eccentric exercises (ie: DOMS causing) was the most effective way to train, we would all be doing eccentric exercises. Some eccentric exercises are good, but it's not common. What's a better way to increase your bench: add more weight and push it up, or add more weight and slowly lower it down? They both might be beneficial, but the concentric (tightening of your triceps and pecs) is what produces the power output and produces gains.