Hi OP, didn't want to read and run. It sounds like there's been, as PP said, too much discussion of specifics about amount of cash gifted, but not enough discussion ahead of time of what might happen in future, and how it might make people feel.
So that's a shame - either lots of discussion would have worked, or zero! But you've got the worst of all worlds.
I disagree with PP who said amounts have to be equal. If not gifted at the same time then there's loads to deal with around inflation and what £1 bought 15 years ago compared to today - it's not actually very helpful.
However, in our extended family we've got a situation where there are 2 siblings, A is very sensible, hard worker, high earner, and B is much more flaky, arty, lives a life with much more downtime! And A is pretty pissed off at their parent's assumption that B "should" inherit more due to being less well-off, when it's life choices not a disabilty etc. On the other hand amongst the in-laws there's an A who has 2 kids and a B who is definitely permanently child-free, and the GPs have been clear that they are gifting A more to support the kids, and eventually pass on to them, and B is cool with that - a very loving and adoring auntie who agrees with her parents' decision.
Anyway, since you're upset I think you should try to resolve this. To do that you'll most likely have to start discussing the un-discussed stuff. I'd start with your parents I think, to thank them but also express your upset about your brother's reaction, and ask their advice maybe? Then once you've talked things out, perhaps you and parents arrange to speak to brother all together to explain/give their reasoning and try to build the bridges back?
It may not work but I think if you leave it, it will just fester. Best of luck.