I did something similar this year, 3 weeks of focus on vo2 (2-3x) per week. Then recovery week and
following that two weeks with high volume with 1x over under and 1x vo2 workout.
To be fair in the final week I was too cooked anyway and cut the vo2 and only did (poorly) the over under session.
I should have probably ended the vo2 sessions after the first block.
Anyhow, result? Meh 
I think for me it might be more beneficial a mixed approach with a vo2 and thr/SS.
It ha been taking me a while to get power back while doing threshold and it has not really improved over last year.
Other info: I’ve been training for 5 years on average of 12-15 hours pw.
This year I also upped the volume hitting regularly 15 hours plus but somehow I fear my recovery weeks were also too easy (6-8 hours due to weather commitments etc).