Do your swim-run focus and just add in 15-20 min spin on the trainer as warmup before 4x runs per week. End each "warmup" with 6-10x30 second hard, 30 second easy. It will have zero distraction from the run focus, and you'll barely lose 5% (if that....I often see my FTP going up because of less overall hours in the winter and the run and swim average intensity being way higher than what I would do during my average biking hours.....which is not to be confused with my hard biking hours). You might gain from the cardio benefits from all that swim focus too especially if you avoid using a pull buoy and do a lot of kick sets too. Also as part of your run focus run hills on the treadmill on steep grades (build up to it)....nice crossover benefit to bike FTP.

At the end of the day, the most important part is cardio. If you can deliver blood to working muscles, you're most of the way there. Sport specificity is the final few percent. Cycling has so little technical component that its the easiest sport to return to and quickly ramp back. Swim and running, you can't really jump back into from "awesome cycling fitness"....easy to do the opposite direction.

Edit: Just to clarify, my FTP may go up in the winter, but my long ride average power would go down if I had to get in the aero for 180K since I don't do that type of specific training. You can't have it all.