I agree you should go ahead with testing if you’re able to. However, I do think your DH is maybe getting a bit of a hard time on here!
As well as the very many positives to getting a diagnosis, it’s also worth considering some of the potential challenges that might come up if your DS does receive a diagnosis. These won’t be the case for every child, but will be for some.
We got our DD (7) tested on the advice of her teacher. We didn’t do it immediately because we were weighing up the pros and cons of a diagnosis at that age. Of course, it’s helpful for older children who are struggling to get a diagnosis as soon as possible, and any extra support that goes with it, but for younger children your DH is partly right in saying it might not make a huge difference, certainly in terms of the practical support provided at that age, and particularly if you’re already doing some of the ‘extras’ at home.
This was depend very much on the school your DS goes to, but for us, despite a host of recommendations in the report, the school have done very little (no resources to support mild to moderate dyslexia - DD does averagely well). She was already doing the extra groups at school with other kids who struggled with spelling / reading., some of whom had dyslexia, some not.
Overall the diagnosis has been positive, particularly in terms of enabling DD to understand why she was struggling so much academically, and boosting her confidence. We’ve discussed all the very many very high achieving / well known people with dyslexia, & made it clear that her dyslexia shouldn’t be an obstacle to her achieving.
However, she does fairly often use her dyslexia as a reason/excuse to not push herself / do work she’s not keen on. If she doesn’t do well in a piece of work, or is struggling to understand it quickly she often attributes it straight away to her dyslexia. And it may well be this is the reason she’s struggling, but it certainly isn’t always! Sometimes she’s bring a bit lazy, or simply hasn’t put much effort it - like all kids do at times.
So we’re constantly reinforcing the idea that whilst things may be harder for her, her dyslexica should not be used as an excuse to not try.