I'm with your husband; the freestanding vanity design saves you from having to move plumbing and radiator to center it, and also will keep the gap from looking wierd. Indeed, the gap will look like a "I meant to do that" feature rather than a "I had to do that" feature. Having that vanity centered/uncentered is one of those things that will show up more on paper than in your real life room. That means that you'll probably notice it (because you're aware of it), but no one else ever will.

I'm planning something similar, so I'll throw out some ideas to get you started. I'd do a 6 ft wide closet with a sliding door and a 4 ft wide bathroom. That will leave you 1 ft of wall space down the center for the plumbing and you can make that smaller if allowable by code and give the extra space to whichever one you'd like. Put the shower along the back wall (kitchen wall), then toilet and vanity. You should be able to fit a 26-ish inch wide shower along the back wall and a 31 inch vanity, depending on code. I say this because our hall bath is 4 ft 9 in by 11 ft, but we have a closet that bumps into the space right around the 7 ft mark, so our bathroom space would be somewhat similar. Obviously, your code might be different, but this might give you something to kick around.

I'd like to see the vanity across from the toilet. That way people using the toilet can immediately wash their hands. If you need to split it in two for multiple person simultaneous use move the shower separate. That would also give you the possibility of a bigger shower. And yes, a pocket door to separate the two spaces. It's all going to feel very tight and small. This is almost what I removed during my remodel of my master bath to make one large room. You're blocking off any light from the window near the toilet to the other space. When I took those walls down the light now floods the entire bathroom and is a huge improvement.

My question to you is: how much do you like your knees? Love this little conundrum. Reminds me of so many awkward little bathrooms that were made at the turn of the century or earlier, Now I'm not a designer or anything and this is with MS Paint (10 pixels = 1 inch so it should be vaguely to scale I hope) so take this with a grain of salt but: I did move your window but if you don't want to move it you can just flip the position of the toilet/sink (though I believe Door 1 is the kitchen door so I left the toilet closer to the wall bc then it'll be kinda out of view if the door is slightly closed I hope?). Not sure if this would work bc I don't have the dimensions from wall to door trim on Door 2 and I'm assuming its the same size as Door 1 this one moved the window again but kept the same layout you have now. I just sized the fixtures to fit the room; same toilet but adding a shorter than average 30" x 54" 2-sided tub (you could probably get away with 60" length though) and a smaller 18" x 30" sink (and I'd suggest going even smaller with the sink tbh, shallow sinks might help in this bathroom) I went a bit crazy for number 3, no structural changes but a lot of plumbing moves! In this one I would suggest a corner sink if thats still a thing or a shallow sink if you're open to it, they're great space savers! The layout you have now is probably the most efficient one you could have in there with the location of doors and size of the room, unfortunately. My ideas at most have about 19" of walking space between the tightest fixtures granted thats all hip height and below obstructions so it might feel more spacious when walking. I've found with the tiniest bathrooms over the years that vertical obstruction height is the real killer since your arms typically take up a lot more space than your feet! Honestly I'm not sure if this is your main/only bathroom (I think so since you want a tub in a space you know is too small for one) and I'm not sure what things you'd prioritize over others (storage, view, movement, basement access, etc.) or if the non-door/window wall can be bumped out a bit, even partially (I assume not since bumping out that wall is an obvious way to get everything you want) Also on the point of barn/pocket doors: do NOT do it unless you have the money to spring for a top tier one and even then I wouldn't suggest it. Yes, they are space savers but honestly they come with a host of issues (getting stuck (pocket), coming off the track (pocket & barn), cleanliness (pocket), etc) and even then they wouldn't address the issues you have with this bathroom What you really need is to close off or move those doors, even moving the full bathroom to a different room entirely, which unfortunately is not possible. Changing the opening style won't give you more room to put the fixtures you want in there unless you want to crawl/shimmy/sidestep past your toilet/sink which I don't think would be up to code! If after all my rambling you're not into that might I suggest taking a gander at the old Sears (and equivalent) home plan catalogues? They have so many tiny and rather confusingly laid out bathrooms like yours so you might have a moment of inspiration! http://www.searsarchives.com/homes/1908-1914.htm (granted some plans don't show the layout of bathroom fixtures but there are some that do like The Chelsea)