Turns out it indeed is.
Finally had some time for tests. 6 normal hits, 8 crit hits.
Before: 684 STR, 347 bonus
Double bonus, so 1365 (closest possible due to SB). 695 bonus. Achieved by dumping 516 points into STR,
684 STR:
Normal - 17034, 18966, 17661, 20243, 17346, 17638: average 18148
Crits - 23748, 25070, 23245, 23879, 23943, 24598, 25124, 24537: average 24268
1365 STR
Normal - 26735, 26806, 23642, 24932, 26799, 24044: average 25493
Crits - 29669, 30012, 30861, 31563, 29147, 28765, 28617, 30675: average 29913
Conclusion - dumping 516 points into STR, more than is available in the entire 200 levels your character can gain (401) netted a 40% (probably too high due to small sample size) increase in left click attacks and 26% increase in critical hits. Seemed about 20 or so % for Pelting Strike hits. Not as worthless as previously thought, but still extremely lackluster.
EDIT:
Larger sample size:
684 STR, 347 bonus:
Normal - 20221, 19805, 22191, 18318, 19807, 21029, 17125, 20810, 16770, 16746, 17450, 21324, 20574, 19917, 16397, 20393, 17115, 20081, 21108, 20101 - 19364.2 average
Crits - 24036, 24347, 24556, 24236, 24394, 25242, 23419, 24062, 25313, 24023, 25402, 24155, 23810, 24676, 24029, 24275, 24107, 24853, 23405, 23809 - 24307.45 average
(Interesting note - for some reason, Critical Hits have a much tighter spread than normal hits. It would seem like a Critical Hit actually causes a bias to the damage roll, so that values closer to the maximum damage of the weapon are picked more often)
1365 STR, 695 bonus
Normal - 25319, 26810, 24278, 24932, 27420, 24935, 26789, 26818, 23341, 24186, 22635, 26533, 27198, 22070, 26848, 22413, 23737, 25660, 24551, 25505 - 25098.95 average
Crits - 30776, 29354, 30503, 31119, 29540, 30866, 31873, 28607, 29910, 29831, 30049, 29982, 28971, 29901, 29525, 29391, 28990, 30366, 30012, 29556 - 29956.1 average
Doubling Strength bonus led to an increase of 29.6% for normal hits (higher most likely due to better armor penetration) and 23.2% for Critical Hits. Didn't do an extensive test for Pelting Strikes, but seemed to be about a ~20% increase by eye. The entire escapade required dumping 516 points into strength. Still will never put a point into STR or DEX unless I increase the attrWdam_fact value in balance.txt.