"Thumb break" designs specifically address the issue, literally unsnapping the retaining strap as your hand closes on the gun's grip. IF that, or a regular strap slows you down, I'd say that's your problem, because it doesn't slow me down any amount worth worrying over.
Every holster I've ever had allows for one handed draw, even the WWII German "luggage case" holsters with a belt buckle type strap can be manipulated with just one hand. The difference is in how long it takes!
Straps are there to keep the gun in the holster until YOU take it out. If you find them too much of a drawback, that's your opinion, but consider the trade offs.
A fraction of a second longer on the draw due to the need to unsnap a strap, versus the possibility of your gun going its own separate way (and out of reach) if you are something other than upright.
Suppose you trip, fall, or have to "dive for cover", and discover that you are now in one place and your pistol is somewhere else, possibly yards away? What is the "inconvenience" of a strap worth, then??