I suggest going to a pet store and trying one put around the store before investing in a leather 4'. You might like it more than I do (slightly different sized dog and person combo, different use cases).
I just tried it out. I can hold the 4' leash with two hands, but they are closer together than when I have a 6' leash, less ergonomic for my shoulders, so I prefer to hold it one handed. YMMV - I have lots of joint pain, so I am very sensitive to tiny amounts of pressure.
If Annie lies down (I like her to lie down when I stop to talk to someone or wait in line) I can only hold the 4' leash one handed. Instead of bundling the 6' leash in my hands, I usually use how far apart my two hands are on the leash to reduce slack- I tend to drop it more if I bundle it.
I used to have a fake leather multifunction leash (stitching broke), and it was hands down the best for urban walking. Two lengths of distance from my hip depending on if I wanted her sniffing, or glued to my side, and hands free so I could occasionally pick something up from the shelf of a store or push a cart without so much worry about where my dog was, but could still grab it with my hand to shorten it further if needed. If the dog pulls, pressure is distributed over the back and shoulders. I have a homemade rope one, and I want to buy a good quality real leather one, but keep cheaping out about the cost.
4' leash is still definitely my go to for taking Annie on a Go train or Go bus - places I need to use a hand to swipe a pass or dig in my purse while the dog is near other people. I also liked a 4' leash for our St. Bernard, who was a bit taller and didn't like to sniff as much as Annie does.
The irritating thing I find is a 4' leash is long enough I need to keep track of and sometimes reduce the length of the leash (needs two hands) but short enough it isn't as comfortable to do so.
I used to walk our dogs in town on an 18" leather traffic lead, and that's another good option for really dense urban areas. I don't own one currently - IMO a multifunction leash keeps the dog in the same position with less care to holding the leash/risk to my shoulders. When I used a traffic lead, the dog was on a pinch or a choke collar, so little risk to my shoulders from pulling.
In the pictures below, the navy leash is 6' (my favourite leash, soft Coastal branded soy). Black and reflective stripe leash is 4' (Ikea leash).
When Annie lies down, need to hold the leash in only one hand - notice how far the 6' leash end dangles- I could easily be holding it two handed. (Annie volunteered to test this out after she found a stick!)
I can loose leash walk with Annie beside me, and hold it two handed, but hands are close together and a bit in front of me.
Two leashes side by side - one handed, there is still quite a bit of slack on a 4' leash for a dog to wander off.
Hope that helps!