Hi there!
Well as i remember, and there is a lot of books and articles about it and all are similar but with diferent aproach, and there is no worse thing than combine two or three methods of training, rather stick to one of it, coz this is not pie in the sky, well you can find power for sprinters, and strenght as a different way to train. There is also diference in what muscle group you use in it, hills are perfect for all of them.
Power training is short max high int. training with minimal rests between series, per example 10x 30 sex max high gear 120-140 RPM-90 sec or so rest easy pedalling, and yes it is good to do leg strenght in gym with about 70% of max weight 20-30 reps.
Strenght training ( specific on bike and in gim) is little bit different let s say 40-60 RPM, someone say even 30 RPM, hill, small hill, or flat, medium time interval and it is depend for what are you train yourself, with longer rests between, per example 4x10 min. 40-60 RPM, 5min or longer rests between.
There is something between for short course triathletes per example 90 min. : 20 min warm up, 10x 30 sec max RPM 120-140, you should fly around 50- 60 km/h, i fly on rolers max 72 km/h, then you are dead, rests 90 or so sec.,
easy spinning 5 min, then 5x5 min. heavy gear, rests between 1 or so min.
then cool down for 5 or 10 minutes
Trashold training, it is something on the border aerobic-anaerobic, per example 3 hours small hills trashold sesion: 20-40 min. warm up 90-110 or so easy spining, 8x15min 80-90 RPM, rests 8 or 10 min between, 20min easy cool down. You can do a short aceleration on 3. or 5. hill to the summit, sitted or out of saddle. You should be feel little tired all the time but not going into red as power training for a single interval.
Aerobic traing level 1-3 this is most important thing, you should spent 70-80% time in season for that and even 90% in base and build up period.
Well first thing you should decide and set yours goals, if you wanna be like Cavendish sprinter you should choose those tipe of training. I think that for us is less relevant discusion about pro training methods, torque etc.
And i dont think that you should train only power without all types of traning unless you train for track 500 or 1000 m race!
As i said before gym training is good and must do, but this is personal thing.
Stay well!