I achieved 3x7miles making this my biggest run week since 2003. I have gone back to just get the miles done comfortably and be pleased with having done them. This is how I used to run up to 1995 and seemed to work, especially for the Ironman in '94. I do believe putting in a few years of just solid running before doing any intervals. The only time I did intervals was '96 and set a triathlon 10k pb of 34min but this was on the back of consistent miles in the the previous 2 years.
Reading a lot of triathlon stuff and read of people running (not triathlon) 1hr 40 half marathons with speed training. I think it is an age when people want results yesterday and everybody has a coach. Most people seem to skip the beginner stage of just concentrating on getting into shape aerobically. The vast majority of people would improve just be doing aerobic training week in week out.
I learnt over the years : consistency, balance, patience, recovery are the keywords speed work is the cherry on top of the icing - you do it when you really have to.