In that scenario I think either could work as long as you can cope with the amount of TSS. However looking at the plans I think I would use the mid volume plan and replace the Saturday threshold rides with the Zwift races.
That way you get the hard efforts racing alongside the sweet spot sessions and a recovery ride which would be a decent mix of sessions, if as I said you can manage the TSS
I did this exact thing last year but took a different approach. I raced a twice a week, a midweek 10, 15 or 25 and a longer 50, 100 or triathlon most weekends.
With that amount of TT’ing, none of which I prioritised or tapered for really as I’m primarily a triathlete and use the TT’s as training sessions, I was getting a large amount of threshold and sweet spot work and I felt that didn’t need repeating in training.
I took the Tuesday and Thursday sessions from the Climbing Road race plan and did one per week so that the training stimulus was as varied as possible. My week for example would be a midweek 10 as a 20m effort (or the 15 or 25 and associated time) plus a 45 min WU and a 20 min CD, a weekend 50 or 100 at tempo or sweet spot plus the WU and CD and a harder VO2 Max effort from the plan. I’d generally ride 5 times a week with 30 minutes doing Volunteer before my weekly interval run as a warm up and a long easy ride as well.
The plans are great but sometimes it may be better in some cases to cherry pick from them to suit your racing schedule. Specificity is obviously important in training to race but in my case I was getting that specificity from those races - I felt I’d gain more from adding in the variety from the training plans.
It took me essentially 12 or 13 weeks to get through the workouts from the 8 week road race plan (I had completed the SSB and Sustained Power Build High Volume plans prior to that so had a decent base to build on) and worked well for me this past season. I PB’d at all those distances this year so something must have worked! This may not work for you and no doubt you’d gain a great deal from following those plans as written but there’s more than one way to approach it which might be worth considering. Just a bit of food for thought.