I worked with IE6 both as it became the defacto standard browser everywhere, and for the years it took Mozilla Phoenix^wFirebird^wFirefox to take hold as the defining force, and then Chrome coming to dominate.
When IE6 came out it was kind of a breath of fresh air... it allowed for a lot of things, and the v4 browsers finally fell off the map. IE 5.0.0 had some hideous bugs on stamped CDs (Office 2000, Windows 2000) that I had to work around for a couple years. IE6 corrected many of them.
Now as things progressed, IE6 became a boat anchor for a long time.. and IE7/8/9 though relatively current at release fell behind very quickly. IE10-11 were also rans in my opinion, and I'm glad most people get to ignore them now.
Nothing compares to dealing with IE4 + NN4 issues... it was truly painful and I'll take what we have today over either. Most people aren't dealing with most of the newer browser features... but for those that are, it can be bad. Safari is the worst actor in the bunch, and they are emphatically not rock solid on that front.
People do forget that IE was legitimately a good browser for quite a while - starting around IE3 it really did quite well. Plus I'll take IE4 + NN4 issues vs IE6/7/8 issues in 20-freaking-14 (or beyond, argh). IE9 at least fixed a lot.
At least the early IE vs NN stuff was fast to change and interesting. IE6 issues were the exact opposite :(
The real explorer issue was that xp refused to die for the longest time. When those browser came out they were kinda fine in context, they got lot of hate a decade later when the world moved onto new standard but you still had 10%+ users living in the past
Not least most of what you mention (other than the 300ms delay) is OS level anyhow.