Salazopyrin is an old drug. I used to be on it and a cocktail of NSAID's - chiefly Celebrex. Salazopyrin is likely to be part of a mix, and not used on its own. Like most drugs used for AS, it was developed for another reason but found to be beneficial for AS. It also takes many weeks to achieve equilibrium in your body (something like 10 from memory), so some patience is required before judging it.
AS is quite an individual thing. You need to find what works. Some years ago I moved the TNF alfa inhibitors (I take Enbrel, but there are others). These are pretty expensive drugs and I presume the availability varies by country. In Australia it took me 3 years to qualify. But I now have nearly normal mobility. Salazopyrin has (from memory - check the drug information) a stomach bleeding risk. This can be mitigated with anti ulcer medications. NSAID's have a higher cardiac risk. All drugs have downsides, you just need to be aware & manage the risks. Personally, if it were a choice, I'd accept a shorter life for normal mobility now. Properly managed AS should not stop you doing anything. But you need a good rheumatologist with whom you have a good relationship and you need to work at flexibility - stretching & pilates.
I'm not going to bother reading the AAIB report, but I'm pretty confident that any contemporary rheumatologist would deny the AS link to inability to look out. If for no other reason than for most people it primarily affects the lower back. It smacks of lazy investigation to me.
One of the main issues with having AS is that its poorly understood both in the general community and by most medico's.
The research on vitamin D is evolving rapidly at the moment. But it looks like most of the population is vitamin D deficient and it looks like vitamin D levels have an effect on the efficacy of drugs. So, I take vitamin D as well. I may do some good, it may not. But it certainly won't hurt.
I'm an engineer, not a doctor. But I like to understand what I take and I have a great rheumatologist who points me to papers to read. So, there are many caveats to my suggestions. Read the drug information, look on the net and above all talk with your rheumatologist.