Getting veggies to go soft in the oven
More temperature?


If after an hour they haven't softened up at all, and this occurs with different vegetables (so you're certainly not just encountering a batch of old, dried out gourds or something,) the problem is almost certainly an inaccurate oven thermostat. Oven thermostats are notoriously unreliable. Get an oven thermometer and see what temperature your oven really is.


  More or less stacking?


for even cooking and optimal browning, you should arrange your vegetables in one layer on the tray. If this were the primary problem, the vegetables on either the top, bottom, and/or in the middle (depending on the intensity and direction of your heat source) would be undercooked while the more exposed parts would be more cooked. 


  More oil/liquid?


Note, oil and water based liquids affect cooking very differently. Water-based liquids will get the vegetables to soften more quickly than oil because water transfers heat more efficiently than oil, and it can turn to steam which is a good medium for spreading heat evenly on an uneven surface (such as a pile of chopped vegetables.) It also kills any possibility of browning because water doesn't get hotter than 212. Just because it's in the oven, it doesn't mean you aren't steaming your vegetables rather than roasting them. There's nothing wrong with steamed veg, but that's a very different end-product than roasted veg. More oil will create more crispiness, but a thin, even coating over all of the vegetables should be the only thing you need to roast them properly.



Now, about that recipe: 175 is low for roasting those types of vegetables. Even without par-boiling/steaming them (which lets you finish them at a higher temperature for more even browning and crispiness,) I'd still go with something around 220. That said, even if the cut vegetables were heavily refrigerated, you still shouldn't be waiting hours for them to soften up if your oven was actually 175. Get an oven thermometer!

Good luck, and happy roasting!