I agree with you on most of those points, Olaus, though, I should mention that the HP doesn't affect build times, but the build speed of the units constructing the building and the time value of the building itself that matters. So if a building with 10,000 HP has the same speed as a building with 1,000 HP, they'll get completed at the same time. The first building might be built in increasments of 100 HP, while the second only increases by 10 HP. Thus, I'd consider the training camp balanced. 50 total resources (and it needs more gold and wood, which are generally also in higher demand for military units) is a fair trade off for less HP.