A bare tank is cleaner than one with substrate, gravel holds more debris than you would think. You can see exactly what you are dealing with waste wise with a bare tank. Try grabbing a handful of gravel out of any tank that has been running for any length of time with gravel in it, you will get a bunch of previously unseen debris in the water.
With the exception of some corys & loachs, which like a sand substrate, and some African cichlids, which do like to move gravel, gravel is only decorative. Anyone seriously breeding has bare tanks, as they are easier to keep clean, and are cleaner running tanks. If gravel were an asset or needed breeders would have it in tanks. It is generally accepted that breeding fish are happy fish.
Bio wheel filters are not needed in bare tanks, and in my opinion are over rated. My opinion is formed from running various filters on a couple dozen tanks, bio wheels sound good in advertsing propaganda, but fail to deliver in the pump & durability department. Form your own opinion from hands on use of multiple filters, not one or two, on a couple of tanks.
Unless you are running under gravel filtration, gravel holds very little nitrifying bacteria, the stuff that maintains a cycled aquarium. In a mature tank you can change out gravel, or remove it, as long as you have the proper filtration.
You do have to vac the bottom, if you wipe the bottom, let it settle, then vac the tank comes out cleaner than any tank you have ever seen. I use a paper towel on fry tanks, a filter sponge on a stick for larger tanks,
Out of my 20 some tanks, 4 have gravel, as they are show tanks. They are a pain to maintain compared to the bare tanks.
My fishroom, 20 some tanks, 800 some gallons, angel breeding setup.