Kevlar is stronger than regular glass, and more wear resistant. It can manage more flexing without breaking, especially if an epoxy resin is used rather than polyester. It’s a blessing. And a curse. In the quest to save a few pounds, the manufacturer will use less layers of cloth ( and less resin) and count on kevlar’s strength to compensate. But this can result in a kayak with much more flex in the hull ( and the deck). The kevlar can manage the flex, but the gelcoat cannot. I have seen many kevlar kayaks with significant gelcoat cracking and spider cracking. Those cracks eventually compromise the cloth underneath, as well messing up the cosmetic appeal.
Not saying this is always the case. Sometimes a manufacturer will use the same same amount of kevlar layers as he would have in e glass and then you will have a bombproof boat. But it won’t be any lighter. And often enough the manufacturer will mix up e glass and kevlar layers and find a compromise between strength and weight, which could be the best solution. But if you are insistent on the absolute lightest boat you can find ( in carbon or carbon/kevlar ) , be aware there is another side to that story.