dieting down can’t be your priority right now. You’re just going to spin your wheels doing that. You’re small, even for physique. You’ve gotta pack on significantly more muscle. Everywhere.
The approach I would take is to try to make lean gains for awhile. A year or more. Try to stay at the bodyfat you’re at now pretty much year-round, but keep adding bodyweight slowly. Eventually, when you have a contest to prepare for, you can start dieting, probably about 4 months out of the show. Like you said, you got smoked at your first one. That’s not surprising.
I would also get with an experienced trainer, and when you’re 4 months out and ready to compete, hire someone to do your nutrition. The fact that you asked the question ‘do I bring in more detail with supersets, time under tension, or isolation work’ is such a strange question that it tells me your knowledge is severely lacking, and reading on the internet hasn’t been sufficient for you to learn what needs to be done.
You also misunderstood my point about your bodyfat. It’s just a number. You will not have your bodyfat % written on your forehead. ALL THAT MATTERS IS YOUR APPEARANCE. What you see in the mirror. Nobody’s assessment of a bodyfat % should affect how you train or eat. The mirror and the scale need to dictate those things.