The absolutely worst two things which happened to Blogger during the last few years are, IMO:

1. What I percieve to be excessive use of JS. You can't even load a blog post there (well, at least, couldn't last time I visited a dot-blogspot site) without an on-page spinner and a bunch of stuff apparently happening in the background.

2. The tld-redirect crap. Admitedly, I had actually thought a similar mechanism to be benefitial prior to seeing an actual implementation of it but I mean, come on, does this not annoy others? What's the advantage of that anyway? Google is capable of geographical load balancing with IP addresses alone just fine, what's the deal?

Disclaimer: These are my end-user reactions. I have never operated at the scale Blogger does so there may be reasons I am not aware of.

Exactly. Blogs are mostly text sites and one would expect such to open at rapid speeds. That's one of the things I like about Svbtle, they load the blog as one single request/response with all the text, styles, JS(barely noticeable) inline making for very rapid load times

I wouldn't say excessive use of JS was the problem. JS provides the foundations to tons of extremely fast websites and should (in most cases) assist with improving performance. I'd blame the overall implementation / design which led to scaling and performance issues.

What I hated about blogger was that for a "group" blog (say, the reddit blog, where different admins might post), any images added to the post get shown from the poster's google account (somehow). Which means if someone leaves the group, the images get hosed.