Aspen's understanding (see her answer) is in sync with mine, but I'll go a step further ... I believe Solumedrol is useful only in the first days of a relapse.
Both episodes I've had Solumedrol, I thought it was great ... I'd love to use it more! Of course, I don't want to feel the way I did to justify its use.
You note "harmful" side effects of the DMDs, and I certainly respect those people (including some I know personally) that don't use a DMD. The side effects of Copaxone and the interferons (one of which I've used for 13 years) are more often considered annoying than harmful, however, and sometimes they're hardly even annoying, so I would urge you or anyone else to try one for six months to start, by that point a person may have learned how to mitigate the side effects as I generally did. I do know someone with Type 2 diabetes that has used Avonex for several years, and it does occur to me that she may have preferred that to Copaxone/others because of the diabetes.
My understanding is (and hopefully someone will correct me if I'm wrong) that IV solumedrol is of the most use within the first weeks of a relapse.
In the area where I live, steroid use for relapse is waning. There is quite a bit of research showing the in most cases, the relapse length is only marginally shortened. Given the risks (blood sugar issues, bone density changes), steroids are no longer given automatically. I would consider it if I lost vision.
One thing to consider -- sometimes the "leftovers" I've had after the acute phase of a relapse actually require me to do something, such as physiotherapy, sleep retraining, or strength training. I'm left with damage that seems like it's still a relapse, but at this point I can make tracks to fix it. Just a thought. Another possibility is that you have an infection somewhere that is ramping your symptoms up.
I'm not sure you would even be considered for steroids with existing type 2 diabetes, although I suppose your physician could address that.
Sorry I'm not an awful lot of help. Hope something here is useful. I did choose a DMT -- I started to get leftover damage from relapses, and the only way to stop that is to stop relapses.