Narrower is easier for assembly cos you can get to things for clamping. If you're making a drawer, and it's 18" wide, or deep, or anything 18", and you have a 3' bench, you can't clamp down. for sanding, planing, assembly etc. Most things that are big can be laid on side, or top.
I have made a split top roubo based on the woodwhisperer / benchcrafted design. It's rock solid, and slightly deeper, perhaps 26", but even with that I lose count of the number of times I have used the split down the middle. It's so useful to be able to clamp something from both sides of the bench.
Also a smaller bench has more chance to go in middle and get used from all sides, very handy.
Personally I put tool on the bench, or on the wall rack, or sideboard.
At the end of the day, what's the right bench is what's right for you. end of. most of the time we work with boards with limited width, but longer. Even making kitchen cupboards of 60cm depth I had no problems with assembly or working those pieces, in fact i found the opposite.
I made a really bad video here:
https://youtu.be/4AsIiyfgGko
if you want a tour of my bench, there are others out there.
I liked Paul Sellers, however didn't want the apron.
I like the roubo split, the end vice, the massive leg vice, the sliding deadman (getting a lot of use now with big panels)
If it were solid across, and it's not that wide, I'd wish I had clamping access holes all the time.
When I had a wider one, against a wall, the back became a mess and I'm not strict enough to keep it tidy, so I had a narrow bench anyway!