Remember that all training intensities are on a continuum, and that no “magic line” has been crossed when you move from one intensity to another (I hate the word “zones”).
Say your FTP duration is 50min (not everyone’s FTP duration is an hour – for some it might be 30min, for others 75min – see Coggan, and the ongoing crap fights on the wattage group about what Coggan meant by “about one hour”). Riding at your FTP for the full limit duration of your FTP will eventually elicit VO2 max – probably during the last 10min of the effort when your breathing is ragged and your whole body is on fire. But, the majority of the duration has been spent on lactate clearance and sustaining that maximal lactate steady state, so that’s were the main training benefits are.
Now, if you sustain a much higher power – say the highest power you can sustain over 4 time 4min on, 4min off, yes, you’ll have to clear lactate, and yes, after a 4-8 week cycle you’ll see an FTP bump, but because you’ve had the throttle down harder you’ve worked the energy demands for short duration effort where lactate rose sharply, even though your pace was steady. You were demanding that your heart pump more blood per stroke, and that your fast-twitch fibers work aerobically to meet a short-term demand, and to burn a lot of glycogen in that 4min time frame. So, that’s where the primary adaptations are.
Rather than getting lost in VO2/FTP/AeT whatever, think of the demands of your race.
Do you have to go really hard for 1 minute? 5 minutes? 10? 20? 60? 360? Train the “go hard” durations you need for your race, and build from the bottom up on the intensity scale. It just works (except when it doesn’t)