If you like to believe that there is correlation despite the longer term trends, then that is on you. You seem to have picked some recent data from the last 3.5 years which seems to be somewhat selective and you are trying to tell a story of correlation from that.
If you look at bitcoin in 2018 and 2019 compared to stocks and then you try to graph correlation over that 5-6 year period what do you get? You get a hell of a lot less correlation because at best, bitcoin is around 3x -8x stepped up from those price points... and yeah you can dance around and try to argue correlation. blah blah blah.. good luck with that.
Now if you add in another cycle and go out another 4 years and you go from 2014 to 2015 and you compare bitcoin and stocks as compared to where they are now, and you have bitcoin around 30x to 50x up from those points, and are you going to want to describe correlation from that data?
We could go back even further and adding another few years (such as looking at 2011-2012(, but sometimes it is not as fair to be going back to data in Bitcoin's very first cycle because bitcoin hardly even had a price, so for sure the correlation is even worse, and it just goes with bitcoin going around 1,000x to 14,000x from then to today.. depending on the starting measuring points.
Yeah, bitcoin has an ongoing unfair advantage over traditional systems because it is still in its early adoption phase which means s-curve exponential adoption rather than the comparing of one mature asset class as compared to another mature asset class, so if you want to continue to make dumb-ass mistakes and try to act as if bitcoin is in some kind of a quasi-mature asset class and blah blah blah, that is your choice to decide to completely ignore that bitcoin is ongoingly likely inside of an early s-curve adoption phase, and even if bitcoin is not guaranteed to continue to prosper within such an exponential s-curve, you are making mistakes by trying to downplay and/or ignore the matter by looking at selective data and trying to act as if correlation exists through your looking at shadows (reflections of reality) rather than at actual light (reality)... but hey, whatever.. you do you.
I completely agree with your observation that with selective historical data can significantly impact the assessment of Bitcoin's correlation with other assets, as different time frames can yield varying results. In this context, I might be mistaken but I think the time frame from 2015 to 2021 holds particular significance, as during this period Bitcoin became well known through the media and prominent financial companies like MicroStrategy invested in it, which led to which led to its value skyrocketing.
While i could be mistaken; it seems that the ongoing unfair advantage of Bitcoin over other assets classes is a significant factor that makes it an attractive investment today. this trend is likely to continue until Bitcoin reaches a more substantial market cap, perhaps $5 trillion or more, which would contribute to its stability as an asset and reduce volatility.