are T-scores 3.5 and 3.9 severe osteoporosis?

Yes, those scores are considered severe. Opinions about how it should be treated varies because a lot of people feel as you do about possible side effects.

I think what we all have to do is weigh the risks and benefits of the various options available to you in conjunction with your doctor. Unfortunately there is no perfect answer. One thing I wish I had known is to ask for how many people experience a certain benefit or adverse effect out of the number treated rather than a percentage. I found later than a percentage can be very misleading.