The question isn't VI in and of itself, but instead how long were the sustained sections actually in L4 and how long were any low power periods connecting those sustained sections?
You basically want to sustain L4 efforts for at the very least 10 minutes or so and during those times there shouldn't be any low power periods below L4 that last for more than about 20 to 30 seconds at the most. The point is to get your body up and running on sustainable metabolic processes and then keep it there for 10, 20, 30 or more minutes per effort, throw in too much rest along the way and you're not really doing the same sort of workout even if the hard periods are hard.
Sure a ride with high power on periods coupled with rests will tend to give you a higher VI but scan the file for low power sections during the 'L4' work to see how many if any were 30 seconds or longer and consider each section broken by more than 30 seconds of lower power (anything below say mid to high L3) as separate L4 sections and then see if these separate sections were at least 10 minutes long.
If it turns out to be a lot of short harder efforts connected by recovery gaps it's still likely a very good workout just more of the SST variety with dynamic riding rather than pure L4 work. IOW, it still sounds like a great training ride but it might not be the best dedicated L4 session.
FWIW, the only time I've been able to do group rides that yielded good sections of solid L4 work was when they included 15 to 30 minute climbs. More typical group rides with rolling and flat sections can be great training for a lot of things but I wouldn't call them substitutes for a good solo L4 session.
-Dave
