I remember when you first came to the thread. A lot of the conversations we had are similar to what's going on with GG.
I totally get it's hard to wrap your head around slowing down to get faster - it took me a while too. My roots are as a 200/400 sprinter. It made zero sense to go embarassingly slow to get faster, but it just flat out works.
GG... Here's my 5K progression. I run next to no speed work. I was/am focusing on nothing but half marathons and full marathons. 90% of my runs are 8:45/mi and slower. The rest are tempo runs with a rare interval session mixed in. I ran 6 interval sessions in 2013.
2010: 26:17, 26:01, 25:47, 24:10, 25:11
2011: 22:54, 22:17, 21:46, 21:21, 21:55
2012: 20:39, 21:21
2013: 20:57, 19:57, 20:08, 20:09, 19:42