Immersion is a personal experience, not something you can simply say is created by a certain feature.
Some people like ground mounts for exploration, some people like flying mounts.
It is about an enjoyable experience, which will vary from one person to the next.
Forced interaction with something a player does not enjoy is not going to make it immersive for them.
Convenience when done right can improve the immersion, can reduce tedious or fiddly aspects that simply get in the way of actually playing.
But in the end it won't suit everyone, so anybody who calls on a certain feature to be a certain way, and against the wishes of other because they deem it "more immersive" is simply being selfish.