Wanting something that keeps away water and that is easily removed with water are competing goals. You won't find anything that does both well.
Vaseline has other side-effects too. It's been my experience that it outright
dissolves the adhesives used inside diapers. Elastic strands come out of leak guards (that can hurt btw), leak guards separate from the inner liner, the inner liner can separate from the shell at the edges, and strands of elastic can come loose in the leg gathers. Vaseline is a wrecking crew for a diaper if it gets to the edges where everything is glued together.
I got a really sudden annoying rash on the inside of my right thigh last week, from working in a hot and humid area for too long. My skin went from fine to on fire in the space of about an hour, it was insane. I ended up with a patch about 1" x 3" that looked sunburned. I tried various treatments to deal with it, but I was somewhat limited by it being outside my diaper's leg gathers by about an inch - anything water-based would get on my pants. So I went with vaseline. Fortunately, it was out of range of my diaper so it stayed together. My first night I didn't have much to treat it with. XP Medical's Absorbency Plus seem to be immune to vaseline's disassembly for the most part, lacking leak guards.
My rash didn't get any worse, but didn't improve either. I only got improvement with some hydrocortizone-based creme. That makes a poor barrier, but does promote healing. five days later and the redness is finally fading away.

It took that long because I could only use vaseline during the day. In the evening and overnight it was hydrocortizone.
BTW, do
not use baby lotion on a rash. The burning I had prior to trying on lotion was VERY MILD compared to the
fire that was set off when I applied lotion. Could not get it off fast enough. But OTOH it gave me a very fresh perspetive of just how bad it
could be hurting, so it was actually a very nice relief to get it washed off and get back to the comparatively mild feeling of the rash.