You're a wee bit misinformed here, in the US when sitting exams like SATs they do have different extra time allowances such as time and a half or double time but the allocation of these is reliant on the persons disability causing them to work more slowly than others. This does not mean someone with ADHD would instantly get time and a half. It means someone with adhd who has poor working memory, low processing speed or poor concentration could apply for these based on how severely they are affected.
Secondly if you did not have any disabilities you would still be required to purchase a laptop for university, DSA is there to cover costs that are caused by your disability that non-disabled students would not have to pay so yes, in an economy where funding bodies are facing cuts constantly , you are asked to pay £200 towards your new laptop, and to pay for upgrades if you want a better one. These are the sort of cost's your student loans are for, we live in a time where laptops and computers are essential for any student not just those with disabilities.
Lastly you sound very much like you are looking down upon those with ADHD who receive help at university? Perhaps you are one of those "ADHD is not a real disorder" people but regardless of that your attitude stinks, the £200 you pay to help fund your laptop could free up funds to pay for one to one assistance for someone with mobility problems in uni, or a couple hours of one to one tutoring for someone with autism.
I agree there should be more individualized help at uni and that the system needs fixing but you just sound like an over entitled brat. DSA is there to level the playing field so that those with disabilities, many people are so grateful for what they get on DSA and your just sitting there complaining that you want more. "People with ADHD get this but I only get this" get over yourself. I agree with what others are saying, if you were asking for extra assistance with studying or notes that would be fair enough but your main complaint seems to be about paying £200 for a laptop that would cost anyone else a lot more.