This is a good example of how it is impossible to please everyone. Can you imagine the whinges QF would get if they attempted to serve special meals (including diabetic meals)
after everyone else? I'm betting that among those with special dietary requirements, there is a higher percentage of squeaky wheels... not to mention the potential 'I'm diabetic and had a low due to QF being to slow to serve me my meal." Serving them with the regular meal service might sound like a good idea, but it would probably be somewhat impractical, especially on wide body aircraft. I doubt the extra time it would take to organise would be worth keeping the majority of pax waiting for their meals.
I was vegan up until about 18 months ago, and I LOVED the vegan meals. One of the best things was getting the meal first, and also getting fresh fruit instead of the canned style little tub of fruit salad (on domestic flights this was a mainstay for a while). The quality and variety of meal was better than offered in some restaurants, especially given that vegan menu options are particularly limited.
It is so much more practical having a special combo meal from an efficiency point of view, and also for spares ratio. I imagine there are a couple of spare meals 'just in case' someone forgot to order, and it would be impossible to have a spare of each special meal. Also, can I risk being shot down in flames when suggesting that we should keep it in perspective? It is great that the options are offered at all, when still many restaurants and cafes don't even offer these sort of options. So you get served first, boo hoo. If you don't like it, BYO. Or do what we did in the old days and eat around the bits you shouldn't eat. If there's the risk of anaphylaxis, make sure you bring an epi pen.