I think there is still value in long rides (4-5 hour) for endurance training. There is still value in saddle time.

First, "base" is not something you develop in an off-season. It is built over years of riding. Understand that a lot of the powermeter trend has taken place on already trained cyclists. The pros have years of riding under their belt; endurance intervals are used to sharpen them for race season and they still do the long rides in the off-season.

The "zones" are complete fabrications by various coaches. Friel and Coggan utterly disagree about where the thresholds of each zone lies if you go by their respective books. I divide my efforts as follows:

• no effort
• endurance pace
• time trial pace
• leadout pace
• sprint

These kind of correlate with the zones, but IMO, the whole deal with powermeters and zones is you are using a precision tool to measure something that is, by definition, kind of mushy. But what do I know. I gave up the powermeter a long time ago and I don't even train with a computer anymore.

I liken training to sharpening a knife. The first tool isn't a steel or even a whetstone; it's a file. Base training, the long 4-5 hour rides for an endurance cyclist, is the file, and I believe this at least partially a muscle building activity. Longer intervals like the OP is suggesting is the whetstone; the shorter and more intense those intervals get, the finer the grit. If you start training with too fine a tool, you'll get an edge, but it'll be fragile and won't last long. If you shape the blade using coarse tools first, you'll get a better shaped edge that can be honed over and over.

The "Time Crunched Cyclist" book even touches on this. That book is for riders to prepare for a single event some months away; it says as much in the first few pages. It'll get you cooking with good form for a few weeks before you burn out and have to reset to a much lower intensity level.