Couch to Sprint Training Plan Questions

If it were ME, I would do the latter.  I know someone here is going to say I'm being callous with your wellbeing not know much about you, but based on your post, if you are comfortable with that kind of millage, I would stick to the longer runs (but maybe two from your week to allow for the s/b) but do the suggested swimming/biking workouts until you see how you progress.  Only running 1 mile twice a week is worthless if you can already do 16-18, IMO

Sounds that you have enough fitness for a slightly more advanced program but maybe not the technique/form you need.  I'm betting your swimming and biking will progress quickly if you can already do 16-18 miles a week running.

Just glancing at the plans, if you can do couch to sprint, you can probably do "original" sprint which may be more up your ally.  It has similar starting s/b workouts but a bit more running.  2-3 miles per workout (based on your pace) compared to the one mile of running in the couch program.

Look at a plan that is based on time for the bike and run as well.  That would mean if your running pace is fast because you are good at it, you will run more.  If your bike fitness is lower, you will bike less (distance wise).

Just my 0.02.  Remember that plans are a great jumping off point but feel free to edit them some.  They are designed for the masses and you may have abilities or disabilities that may need them to be modified.