What to do about strength work depends on why one is doing it. Recreational riding, maybe with groups? Long distance? Racing - - crits, road, stage, track? Touring? If you're doing it for cycling, do you focus on sprints, climbing, flats?
If it's not for cycling, then health, running, backpacking, skiing, or appearance?
There's probably a different answer for each of those.
If this is for non-racing cycling, all you really have to do is squat bodyweight, but you're already past that. For the leg press, one-leggeds are the usual prescription for cyclists, whatever their specialty. You can do whatever and it's not aerobic.
I don't find leg curl and leg extension useful for cycling, or any isolation exercise for that matter. One thing that most folks don't work enough is calves, especially high rep calves. No HR issue there. I work also them one-legged to make sure I'm symmetrical. Another thing I see frequently ignored is reps. Some folks do 100 reps on the leg sled. That's a whole new world to explore.
The whole idea of strength training is to get tired. What weight one needs to achieve that goal is totally immaterial unless one is competing.
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