SJ21, reading your post, I think I can sum it up with a 5 word question - "where is the die cast?"
The fact is that as economies have gone downhill, costs have needed to be reduced in some ways. I have yet to have my Soundwave turn up, but from what I've experienced with Red Alert and Soundwave, they tend to be a little more hollow and thanks to being all plastic, lighter.
Also I think the problem with Laserbeak is the size of some of the joints and the stresses they're placed under (specifically the connector struts for the turbines). I will say that with the exception of the Cassettes and maybe one or 2 of the Minicars, that shouldn't be a problem across the line.
I think there's a fallacy in your reasoning though. There are plastics and there are plastics. The fact is that some plastics these days are more durable than metals. Heck, when spidersilk becomes commonplace, it'll be much thinner yet so much more durable than kevlar.
The days of thinking "it it's not metal, it's more brittle" are coming to an end. The MPs might be all plastic, but honestly, I've noticed the plastic is generally of excellent quality and so I'm not convinced it's a trade down.
Overall, I love the new direction being taken and I can't wait to see more of the same