There is a huge difference in the quality, workmanship and usually also in the design quality. Obviously some of it is the prestige of the brand, it would be stupid to pretend otherwise.
I feel great when I carry a designer bag. I kind of wish I’d never got my first one, though, because I could never go back now (not entirely true, of course I could if I absolutely had to. And I do buy from places like Jigsaw/Jaeger/Whistles/Reiss/Toast as well, particularly for workhorse bags).
However, on the other hand I’ve had my first bag (Anya Hindmarch Belvedere, original style) since 2014 and it still looks brand new. I will likely keep it for the rest of my life. My second was a Mulberry Mitzy East West hobo that I had seen someone carrying and though ohh I like that, looked it up and it was no longer in their current stock. I found it a couple of years later in their shop in York and got it for a much lower price. I still love it, and it also still looks brand new. I’ve got a couple more and aim to get one more per year if I can.
Bags make me happy, and a beautifully crafted bag is a thing of true beauty. I don’t go out much, don’t usually go out to eat or drinking at the weekend, for example, so this is where I spend that money. And I get something beautiful that I can keep forever and that gives me joy.