I don't disagree with your thoughts at all - design and appreciation are wholly personal things. For me, I look at the odd little fold-out legs at the back and think 'what were they thinking?!'. The 100-series supports were just perfect, the 500's look like the afterthought of a junior in the design lab 2 days before the production run began.
The balance of the 500-series is different though. That swopping shape may look nice, and it may sit beautifully on a desk (and actually, it does!), but on my lap, the thin front where it curves down, and the thick front of the display when it is open, tends to make it feel unstable on my lap when I'm using it. In fact it bounces as I type on it as a result, so the 'feel' isn't helpful at all.
The 100/190/5300 brick-shape is far more stable in this situation, so I find it far more workable. It is personal though, which is why I said that I am probably a difficult user, because the way a system feels in use is crucial to me in ways it likely isn't to many others.
Performance wise, it is certainly true that the 5300 is disappointing compared to other models of the era, and it is impossible to justify Apple's design choices in any context other than bad management, serious cost-cutting and poor financial results perhaps, but I have the luxury of not having to consider this at all, since if I were to be decoding MP3s (for example), I'd just pick a system which can do that task well. What I need is a system that sits exactly where I put it, provides a stable surface to work on for hours at a time, and has a consistency of behavior, particularly of the keyboard.
My 145B is very close to that, and with
@Siliconinsider's RAM expansion, it can now run what I need it to, which is great (or will be once it is recapped), but I've been trying to find 'the perfect' alternative ever since, and in my use case, for various reasons, nothing hit the right spot until I got the 190. It just works. The 5300 by comparison is way faster at what I do, so is an improvement. If I was working at a desk so weight not being a problem, my PDQ would be the go-to of choice, but it's too heavy for use on the lap for more than an hour or so.
I am a very fussy user, but perhaps not fussy about the same things as other are!