Not trying to conjure a debate on this, but I'm curious as to what are the mechanical blocking benefits with longer arms ?
Maybe I can see more horizontal blocking area that makes it harder for the D to get around the block, but I also think that with longer arms they are perhaps more likely to grab or extend beyond where they should and get called for Holding.
Regarding your 2nd statement ....
With regard to pass blocking, there is a strong effort (usually always) to execute a pass play that allows the QB to find a Receiver and release the pass ASAP. My thinking on this is that the Secondary is more vulnerable (not reaching for an interception) and the 'QB protection zone' is more secure within the 1st 4 seconds after the snap. Obviously this quick release effort allows the O line guys to end their pass blocks sooner.
With regard to a run play, they attempt to maintain their design block pattern at least until the RB is beyond their own position. Any effort to block after the RB has run beyond their own position will likely trigger a Clip, unless they are directly trying to push their own RB across for a 1st down or the Zero-yard line.
Not sure any of this explains why SF Inc is looking for taller, leaner guys; other than maybe they can keep better pace with a quick tempo offense. I'm not sure I see an obvious benefit to the taller, 'lankier' O line guy with regard to better blocking mechanics.
I'm very curious to see what others have to say about this topic regarding a taller, leaner O-line guys .... why go that direction ?