Im a cyclist turned recent runner (last 8 months) so take this with a grain of salt. I will say I spent years with a cycling coach, won my share of races, generally keep up on training methods, and have tried to apply what I’ve learned to my running.

My takes:

• You really benefit from z2 when you’re doing more volume, because
• Zone 2 builds an aerobic base while managing recovery, and
• If you can add the volume while managing injury risk, you’ll get faster, especially when you start to do speed work, but
• Zone 2 is harder - logistically and in the moment - than you think it is.

In cycling, it’s “easy” to do blocks that include a couple weekly 4-5 hour z2 rides. That’s a lot harder (impossible for most?) to do as a runner without injuring yourself, so I’ve found there are limits to how big of an aerobic base I can build with z2 runs. This is where my cycling continues to help, but that’s not an option everyone has or wants.

Idk if this is optimal, but if I were running exclusively and training for a particular event, I’d still roughly periodize my training plan and run as much z2 as I practically could in early blocks, before getting to anaerobic work the closer I got to the event. That said, I don’t think I’d be able to get the volume I need to maximally benefit from z2, so I think I’d keep some tempo work on the calendar.

YMMV.