I only have a canister filter and an AC110 and my water is CRYSTAL CLEAR TOO, if I removed the HOB, I would still have crystal clear water. Crystal Clear water can be had by any filter so that in and of itself has little or nothing to do with having a sump. I think there may be some benefit to using a sump such as increased oxygen for bacteria and keeping items out of the display tank though it's not much of an issue really. The amount of biological in a simple HOB filter is more than enough to keep the ammonia and nitrites 0. Much of the sump hype we hear is just that hype and personal preference. The pumps used in a sump are more expensive in terms of watts too. Sumps are for people who like to tinker with things and don't mine expensive utility bills. I may build one someday just to see what all the fuss is about. I've read others who switched back to canisters from using a sump and said it wasn't worth it. Personally I think the simplicity of the HOB filter is where it's at, simple is always better.
I guess I'm a tinkerer and like expensive utility bills
Seriously, I run all 3 setups. My 300 has a 75 gallon sump, my 135 has several canisters and my 60 has 2 hobs. The main reason I went with canisters on the 135 was 1)tank wasn't drilled and 2) I had a bunch of canisters looking for homes after I built the sump for my 300 lol.
I look at it from an entirely different perspective though. Any of the the above filtration styles will work. Some are cheaper, some move more water, but like you said all will effectively "filter' your tank. But once it's setup, it's the maintenance and aesthetic parts of the equation that's most important to me. A clean tank is a healthy tank IMO and the easier it is to maintain, or clean, the healthier your fish will be.
I use xp3's on my mbuna(135) setup. They are by far the easiest canisters I've ever maintained, but it still takes about 20 minutes or so to pull one, move it to the tub, rinse the pads, fill and reinstall. I run 4, so each month that means about 40 minutes of maintenance, as I clean 2 every other month (mbuna are poop factories)
On my 300 with the sump, I run a pair of 7" socks that seriously can be changed in less than 2 minutes for the pair. I change socks at every water change which means 8 minutes of mechanical filtration maintenance a month. For almost 3 times the water volume......and one more important thing to consider if your ocd like I am........the sump setup has no mechanical parts visible at all. A completely clean setup in more ways than one.......
But ultimately my emperor 400's on the 60 are almost as easy to clean as the sump. Takes about 2 or 3 minutes to rinse the pads and I'm good to go. Can't hide the intake tube though, which personally drives me nuts. Even on the mbuna setup with 4 renas, I've found a way to practically hide all in take and outputs so it's pretty clean. Every time I look at my 60 i see the 2 intakes and it just doesn't look natural to me......
So, if I had to do it all over again, I'd always do a sump. Larger area for bio and mech, larger water volume, more room to hide heaters, airstones, etc , and is by far the easiest and quickest to maintain. And with a 50 micron sock, water quality it's by far the clearest.... housing the largest fish.