Is lifting heavy the optimal way?

I've been lifting for about 5 years now, and I've made so many mistakes along the way, especially in my early years. I would always prioritise "mind to muscle connection" with high reps but low weight (around 15 reps x 3 sets per main exercise), and even though I got sick pumps and I felt muscle fatigue after leaving the gym, it never amounted to much. I weighed the same and looked the same for years, never really getting stronger or being able to lift heavier weights. I was stagnant because I never really went heavy.

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It wasn't until I decided to just go full heavy and do only 6-8 reps to failure for 2 sets did I see a much more noticeable changes to my physique. The gains that took me a year to develop, I was now seeing in a matter of months. I started to eat more too, since lifting heavier naturally made my body hungrier than before. Sometimes I even ditch proper form/mind muscle connection if it meant that I can go a few extra reps on a heavy weight to total failure.

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Is this truly the optimal approach or am I just experiencing newbie gains that I missed out on my early years?