Holding a pleco or large cat in those ways does not distort any part of their body beyond its normal limits; as long as the heavy cats have their weight supported, no problem.
But those three bass pics show the spectrum of typical holds that are commonly seen. First pic, that mouth is about as far open as it really should ever be, and much further than required when the fish is in that position. Second pic, that looks great; fish is controlled, mouth is merely open...not distorted.
But, man, that third pic displays exactly the bad practice to which I was referring. You're supporting the fish's weight, even though that fish is not heavy enough to worry about holding in a vertical suspended position...but you still have the lower jaw cranked open way past normal. Look at the acute angle the jaw makes to the fish's body, right in front of your index finger. That is not normal and is not doing anything good for that fish, and it isn't making it any easier to control. Bass don't have a nuchal hump; in that pic the entire head is twisted downwards to such an extent that it appears this one is trying to grow such a hump.
If your hand were rotated 180 degrees downward, the hand by the tail would be unnecessary, the fish's body would be hanging comfortably vertical, and the mouth would not be so severely distorted. The fish would still be comletely under control, but would not be forced into an unnatural and potentially damaging posture. There is simply no reason for holding a fish the way it is shown in that pic.