I mean, I used to have a Mercedes AMG before my current one, and it was simultaniously the worst and the best car I have ever owned. The worst because it was uncomfortable and built like a horse cart, everything in this brand new, very expensive mercedes creaked, rattled and squeaked. I've been back to the garage so many times for "minor" fixes just to make the car usable I nearly ended up hating it after the first year, then kind of ended up learning to live it and started enjoying it more. Which brings me to the other side - I loved the way it drove, it was like the extension of my mind and my body, it was like glued to the road and like a rocket if you wanted it to be.
So yeah, I totally 100% get how you can simultaneously love and hate a car, especially if it's an expensive one.
GLA45. Which yes, is nothing more than a fancy A class, so some excuses I've heard were "well, it's a 'cheap' AMG, what were you expecting". I don't know what was I expecting, maybe only that a £55k car won't have crappy plastics everywhere that creak every time you go over any bump.
Having said that - I've spent enough time on AMG forums to know that the same problem exists even if you buy a C63 or E63, the build quality of the interior just isn't great(while the mechanical engineering arguably is, those cars are very reliable when it comes to the actual mechanical bits)
But yeah, that's a weird segment that car is in. It's expensive, because the engine is expensive, but at the same time you're getting the exact same interior and fit-and-finish as the non-AMG versions of that class, which means an AMG S-class is very nice, while an AMG A-class is just not very nice at all. So yeah, your experience sounds exactly like what I would expect out of that specific model, and by just looking at the price tag, it's not very intuitive that that's what you're gonna get.
So yeah, I totally 100% get how you can simultaneously love and hate a car, especially if it's an expensive one.