That icon only works half of the time for me. It doesnt show me the latest post it shows me the last post ive seen if Ive seen the thread before. Arguably better.. but some would want to just skip to the end.
But in a thread that you're actively following and want to see all the posts, sending straight the your last read post is the best option. And from there, if you want to go to the last page it's a simple click to the last page and scroll to the bottom.
On the other hand, if the default was to go to the last post I would get really frustrated because I like to read all the posts in the threads I follow, so there wouldn't be an easy way for me to do that.
And of course, adding another button to do what you'd like might work, but seems like it would get cluttered with extra buttons and would be even more confusing.
I do see where you're coming from though.
I just wanted to ask the same right now. It would be great when using the spy that you are directly redirected to the latest post and not the first one.
There a little icon to the far left that does that already. It looks like this: Show Image
Heh. It took me wayyy longer than I'd like to admit to realize that this button existed... :-[ I came very close to making a thread very similar to this one, and right before I did I discovered that button. :))