Trying to understand the graphs. Vcore 3.1 300

For the last week, I've been watching countless videos on input shaping and understanding the graphs. I did my best to tension my belts equally and my prints actually come out really good when I set my acceleration to 12000. However, looking at my y results, why is the acceleration recommended significantly lower? I've also attached my belt tension graph. This was my first graph after countless 10+ prints. Is there any adjustment I need? I feel the belts are to tight just now. But they feel loose compared to my voron. Any advice or recommendations is appreciated! Thanks, Marc.