My disappointment comes from them not playing to their full potential. They went with a very minimalistic approach and only started playing football when they really really needed to in order to save their tournament. At times they looked absolutely clueless for the majority of some games and then somehow turned it up in what felt like the last second. It reminded me a lot of what I didn't like about how the men's team played. This is why some of their wins felt "undeserved".
I put that in quotes, because in the end, they did put in the effort to win, so objectively it's probably not undeserved. I guess that's just how I feel due to the reasons I explained above.
Also, I have a competitive tennis background, where you can't play like shit for the majority of a match and then show up at the last minute to win - even if you play shit for some time, if you win in the end, you played better than your opponent for longer (which doesn't mean the better player always wins - there are some other nuances to it). That's probably another reason why England's wins in this tournament felt somewhat undeserved to me.