At 5'6", 29" inseam I have similar problems with pants.
No off the shelf mixed use pant will ever have the knee pad set in exactly the right position to protect in a fall. Mostly, especially for shorties, the pad is OUT OF POSITION. I've used dirt bike strap on knee pads for 20 years now. I customized mine, adding quality impact foam (boxing head gear). The pad is always there, exactly where it needs to be in a fall.
YES! more to do, but once on, the knee pads stay in place most of the day. For commuting I'd use the built in pads and just take the risk, but you may not land on the pad if you come off the bike. Down side of strap on? After a week of sweating ... they STINK!
Those Cortech pants look more suited to colder, wet weather. Just because it says "breathable" does not mean they will feel cool in hot weather, they won't, they'll boil you alive. A couple side vents won't help all that much. Leather or jeans is cooler. (serious!) Cordura and such fabrics really get HOT, don't shed heat well. They do look fine for cool/cold, wet weather and quite robust as well.
Good quality Mesh gear is more verasatile, it's cooler of course and when cold, add under layers. I have several pairs of riding pants, I use the ones for the weather I've got. On long trips its a tougher choice, but even there I'm carrying two pair. (a pain, but means I've always got the right pants on hand)
Read the above thread about knee pads, armored shorts. All good, especially off road. On road wear your Kevlar jeans (good choice IMO!) just slap some knee pads in there.