Compared to most of the veteran feats, body weight training is quite good, since you can reach 10 str at character creation, and lots of characters have high strength. Bodybuilding requires 12 con and only gives an 80 health boost. Expert sprint requires 13 agi, and only gives a 10 ap boost when sprint is activated. Veteran feats are meant to be niche feats for specific builds. Nimble is better than body weight training because it is the feat that enables evasive builds, so it needs to be powerful and available early. The advantage of body weight training is that it stacks with nimble, which can let you wear heavier armor while retaining low armor penalty bonuses.
That's all well and good, but it does not change the fact that BWT is, quite literally, just a downgraded version of nimble. At a higher requirement cost.
Expert sprint has a high requirement but it is a straight upgrade of sprint. Not to mention that 10 action points is not a negligible amount, and neither is 80 health.
But when it comes to BWT, you've literally been going through the entire game without that 10% less armor penalty, waiting to get BWT, and when you finally get it it just feels like such a let down because of how little impact it has at that point in the game.