>>280549605It was a common consensus even when Brotherhood started airing, since there really wasn't that big a gap between 2003 ending and Brotherhood getting the greenlight. It's not very subtle about it either, or else why would Brotherhood's first episode be a non-canon fanservice battle with a bunch of characters that hadn't been introduced yet, and why would they alter the early fights like Cornello getting a huge power boost? Brotherhood's biggest problem is that it doesn't want to "bore" the people it assumes already know what happens up until Greed's introduction, so it either sprints through it all or tries to go bigger for no reason. If it didn't assume viewers had seen 2003, it wouldn't have those issues.
Like most people, OP, I say just watch 2003, then Brotherhood. When you get to Brotherhood, you can just skip to episode 11 or so if you want. Both of them are great shows, but have flaws on opposite ends. 2003 has a rough ending, and Brotherhood has a rough start, but neither of them are ruined because of it.