DG,
I'm not trying to sell you on anything, just explaining & trying to answer your questions.
Over the past three or four centuries people have accomplished various goals with various guns using beads (even on handguns) and fixed sights.
It's entirely possible to achieve solid hits at different distances with different platforms using fixed sights.
It is not, however, particularly efficient across the board.
I've used fixed sights on duty handguns and never had a problem qualifying.
In some cases, the issued cartridge of the day did not match up well with where the sights were regulated, but distances (25 yards max) were close enough that it didn't matter all that much. With some Alabama Overunderage I could place hits in center mass well enough to score.
When circumstances allowed, though, I did appreciate the ability to zero the duty gun using adjustable sights in mating POA to POI.
It just required less work.
It was also a nuisance at times in switching around from gun to gun in trying to remember which one shoots where relative to POA.
I like to, wherever possible, regulate my adjustable handgun sights to print the same place at 25 yards from gun to gun. Again- simpler & less work.
My father several decades ago switched from a fixed S&W Model 10 to an adjustable Model 15 at work after getting tired of having to adjust himself from load to load, instead of adjusting the gun.
Yes, you can, with sufficient familiarity, develop workable skills with a lesser sighting system, but as distances increase it does involve more work, and more guesswork. That can increase when switching to a different load that doesn't perform the same.
Even with adjustables there's still some need for experienced "guesswork" at varying distances, but once zeroed to put a slug in a specific spot relative to your sights (at 50, 75 or 100 yards), you have a known standard of performance for your gun & load, along with repeatable points of sighting reference to line up your eye with two sighting points that offer infinitely better consistency than trying to center the bead in the same place on the receiver top grooves and trying to find the same bead elevation above them.
Brennekes or saboted bullets are probably better reserved for shotgunners who are more into an advanced level of accuracy on a regular basis than the casual shooter who throws a few downrange each year, like you. And that's no insult.
The Brenneckes & the sabots are high-performance loads, and if you don't need high performance & don't have a gun set up to take full advantage of it, there's probably not much point in spending the money.
Denis