Perhaps a simpler way to think about it is, ‘what is the goal of this plan’ as opposed to ‘what is the goal of this workout’.
You’re in base phase, so you’re trying to adapt your body to long(ish) efforts so you’re trying to build strength and endurance to prepare you for build which is an attempt to increase your FTP through more varied efforts but with more consistent time spent at and above threshold.
Thus, the primary goal for where you are now is the foundation for more important threshold efforts in the near future. The reason you’re doing some VO2 max and threshold work in the lower volume sweet spot plans is to supplement your comparatively low volume and still build your aerobic base. So…do whatever will further those goals while still permitting you to have fun on the bike on your outdoor rides