Because the term "underhand" is a well-established name for a two-handed cast, and "Pendulum cast" is a well-established cast for conventional casters and in fact a technique that is popular for tournament distance casting with level wind reels (try Googling it) - I'll use the term "inverted loop" for this type of cast personally for what that's worth.
Per the article - Paul mentions the upward flip at the end of the cast hitting the trees from below, which is not shown in your diagram. So each technique has it's own liability with respect to the obstacle.
Personal experiences aside, I would expect that since most casters have developed a feel for the path of the upper loop (thus the fly) from many thousands of casts, given a sampling of 100 capable casters putting a fly under a branch the standard casts made with a sideward tilt would result in less snags than the same 100 caster's attempts at an unfamiliar inverted loop.
I would also expect that both the experienced inverted loop caster and the tilted overhead loop would result in some hitting of branches, and as a fisherman first (vs. caster) I would reposition myself and drift the fly down into the spot before resorting to such a cast.
Any amount of whiplash at the end of a horizontally tilted 'normal' cast would miss the branches in the diagram shown.
However, if someone has invested the time into perfecting this with a modicum of control I could see how it would offer another weapon in the arsenal but more so when the branch or obstacle is between the caster and the target rather than above the target as shown, because the leader does not unravel in a perfectly straight plane at the end of the cast as drawn.
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