Thought I would chime in here to the post because everything in this thread is very interesting to read. One advantage that you have is that you have a hardtail and don’t have to worry about the rear shock or anything like that. Even though I ride both FS and HT, I like the HT on climbs anyday!
I had a heck of a time at the beginning of the riding seasoon this year with hills – probably because of the long winter break, but I hated being the one in the back getting passed by other riders. I would catch them on the downhills and more technical sections, but the uphills were grindingly painful! I started doing more cardio exercises and put more miles on the road bike to get my aerobic up to speed. MTBing is a combo of aerobic and anaerobic so to find the balance between the two is key. I started hitting the gym more and working on some weight training to help those sections where you have to dig deep to get over rocks, stumps, etc. One of the main things that has helped me has been loading up my camel back with some weight plates and running hills or running stairs. It helps to have that extra added weight for your legs to really work getting up the side of a hill. I also take a nasty hill climb and just continue going up it as hard as I can. When I reach the top I come back down and do it again. If I have the time, I will tackle a hill about 3 times to make myself work. There is no shame in granny gearing up a hill just to make it. While flying up that hill would be nice, I realize that I am not a pro MTBer and just a guy that likes to have fun. My goal is to just make sure I am not the last one in the pack on group rides! I do the same thing on my road bike in finding a nasty hill and just trying to attack it as much as possible.
Anyway, riding should be fun and ever since I got into XC racing I often times lose sight of the whole fun aspect of it all. Most of my rides turn into training rides and I really need to step back and remember why I started riding the trails in the first place.
Hope this helps. Enjoy riding and you will be climbing like a pro in no time!!