Check out my recent post about VO2 Max workouts here. I think it could be worth a read.
Not all VO2 Max workouts are designed to simply increase stroke volume through sustained time spent near VO2 Max. This is a power zone just like Endurance, Sweet Spot, and Threshold, but the name tends to confuse people. For example, with Threshold, the power or training zone is a range (95-105% of FTP) that covers the rough area around your estimated LT2. Similarly, VO2 Max as a power or training zone also covers a wide range (106-120% of FTP) and there are multiple types of stimulus that you can target while riding in that range, hence the many types of VO2 workouts.
If the VO2 workouts you’re being prescribed are too easy, simply finish them and fill out the post-workout survey properly and we’ll make the necessary adjustments down the road. There are plenty of hard VO2 Max workouts in our library. 
The issue I see with your approach is that you’re not actually doing 90% of the workouts we’re prescribing to you, so while you think that what we’re giving you is too easy, you’re not really giving us a chance to suggest adaptations based on your performance. If you’re not following the plan, the specific workouts that we’re prescribing are pretty much meaningless other than that you can see one is a VO2, one is a Threshold, and one is Endurance so that you can find your own replacements.
Rather than using custom workouts or finding random placeholders, I’d recommend using Workout Alternates to find harder workouts when you feel the need. The workouts we suggest there will still respect the plan settings which are based on the discipline of your plan. This ensures that you’re specifically working towards your goal with relevant workouts.