- It is no less concealable than the Glock 19
He's right, basically. The standard-capacity G26 is no less concealable than the standard-capacity G19: it's just more so.
- It is impossible to grip ...
He's incorrect. The statement is untrue, unless one's definition of "grip" consists of only a full, four-fingered grip, though many with fewer fingers on the gun "grip" it just fine.
- ... if you add a grip extension in any way, it makes the grip the same size as a Glock 19
He's right. Grip extensions make the G26 very close in height to the G19.
- It has a shorter barrel length which is not really a problem ballastically ...
He's waffling. A shorter barrel will have lower ballistic punch, in proportion to how much shorter it is than the larger alternative. Whether one believes it to be a problem depends on one's point of view regarding minimum effective on-target ballistic "punch."
- It has a shorter barrel length ... but it makes the line of sight shorter and thus aiming less accurate
He's right, in that a shorter sight radius toughens the aiming problem. Though, whether it ends up being less accurate will depend on level of comfort/training and how well it matches the shooter's "sweet spot" (balance, weight, timing with the shooter's technique).
He's right. If comparing the two for their design appropriateness, a standard G26 sub-compact holds fewer rounds than a standard G19 compact. If one opts to acquire separate non-standard-length magazines, then both the G26 and G19 can end up holding the same number of rounds, though I don't imagine this is what he was getting at.
- His conclusion. Why carry a G26 when you can carry a G19?
He's making assumptions, based on his personal criteria for him personally. But that ignores what benefits others find in the G26 over that of the G19. Many find a G26 to be more concealable, of sufficient accuracy, of sufficient capacity, and lighter due to reduced size and capacity.