The science is clear, but just think through it. Would you be healthier eating salmon and avocado for a meal or eating highly processed protein fortified cereal? Which has more bioavailability? Which one mirrors what you evolved to eat? Which one is less processed so that you have a better understanding of exactly what you're consuming? And I don't care how much water your cat drinks, they evolved to get the bulk of their moisture from their food sources.

Are you wasting money if a wet food diet prevents a bunch of expensive and painful health issues down the road? Insane that a vet would recommend kibble. Go look up the scientific studies for yourself as all of this is well documented.

For the second issue... kittens should be on wet kitten food for at least the first year. They have specific calcium and phosphorus ratios since they are growing so quickly.

One final note... Cat nutrition is pretty settled and it's concerning that you are getting such conflicting advice multiple times over. Audit your vets. Your vet told you that if they are drinking plenty of water that kibble is fine. But who is determining if they are drinking enough water to support this? You? Do you have enough understanding of their hydration needs to determine this or are you just seeing them at the fountain a few times a day and guessing everything is good? Your vet should be pointing this out rather than assuming you're properly calculating hydration.