Well, for something that you've been told/read/heard is low efficacy (no idea where from, I'm just accepting what you have said), I think 100% success rate in not getting flu at all both whilst taking various immune suppressing medications (methotrexate, Humira, steroids, hydroxychloroquine, etc, etc) since I was first eligible for vaccination, is pretty good.
In addition, there are the aspects of the overreactive immune system creating cytokine storms in response to influenza infection and the subsequent exacerbations of AI disease after infection.
Any autoimmune disease puts you at risk of having another AI disease diagnosis in the future - T1 Diabetes and Celiac Disease, Sjogrens and RA, RA and Uveitis, Psoriasis and Psoriatic Arthritis, Parathyroidism, Scleroderma and Lupus, any of the above with IBD - they're all frequently comorbid. Which doesn't mean they caused by vaccinating against something that is highly likely to cause severe illness in itself.
A mask won't - can't - protect you. They're supposed to be to protect others from you. Largely staying in isn't living in a sterile bubble as though you're in a negative pressure hospital room following bone marrow destruction or working in an underground laboratory on Smallpox research - you'll still be outside at times.
Of course, an opinion is an opinion. But in mine, from lengthy experience, there is no way of ensuring you cannot come into contact with any virus that is transmitted in the way influenza is. The best you can do is take the protection that is offered to you because it's better than none at all. And then you can be like a twat like me - having direct physical contact with 10-45 people actively shedding flu virus every day at work last winter and, despite taking biologics, be absolutely unaffected by it all.
I'd also recommend that you press for your AI disease to be properly treated. I've still been able to access treatment - I'm sat here waiting for my new biologics to be delivered at this very moment and I've been told to call the nurses' number during the transition process at any time if I feel I'm not improving enough or flaring more and I'll be able to access an im steroid shot through a face to face appointment within 7-10 days.
I think, having had both AI disease and influenza, along with having had vaccinations (side effect - slightly tender shoulder when pressed for 3 days, solution - don't press it, then) and been able to sail through every flu outbreak in recent years - except the couple where I hadn't been able to get a vaccination in time and was incredibly ill as a result - I think the lack of efficacy/maybe it'll cause side effects argument is weaker.
Just wish I could bloody get one now. They're not available in the area yet and I'm on the waitlist with five pharmacies and the GP now, as I'm getting genuinely worried with the numbers of kids at work coming down with flu like symptoms (not Covid ones, and I've probably already had that in March).