That’s enormously overstating the case. Spelljammer is flying a magic boat between worlds. Allowing it to go to the Feywild, a thing that literal first level characters can do on accident, does not remake the setting.
It will change. Of all the settings, Spelljammer and Planescape can’t avoid being changed. Even if wotc wasn’t doing a unified multiverse this edition, Planescape and Spelljammer wouldn’t exist in a contradictory cosmology. Because of that fact, they will be retrofitted into the current version of the great wheel, complete with Feywild and Shadowfell.
Making parts of the elemental planes, and a few other places, accessible from Wildspace, is very much in keeping with the multiverse as presented in 5e.
Your comparison is patently absurd. Age of Sail to planar travel? Seriously!? Space travel to planar travel would at least have been a vaguely appropriate comparison.
But even if I’m charitable, and use space as a comparison instead, it doesn’t stack up.
It’s like claiming that Star Trek completely c changed what made it Star Trek to the point of not being recognizable when they introduced the Mirror Universe.
And even then the change is less in the case of Spelljammer, because in D&D canon planar travel is a known thing. Other planes aren’t theoretical, and there are cultures that actively engage in it.
The hard separation of the two ideas has always been weird and forced.