Alexa is dead, those are false numbers. To be honest, I wouldn't rely on statistics given by those websites.
well you could be correct I have zero idea how to know website traffic reported is accurate.
How about if I sign in and out of this website 10 times an hour daily does it count at 240 visits or 1 ?
Some website owners have Google Analytics code on their website that counts traffic and many other useful data. Then these website owners connect their Google Analytics to similarweb.com and data acquired via this way is accurate but I highly doubt altcoinstalks or bitcointalk does that. So, when website owners don't connect their GA to similarweb, then the only way for similarweb to collect data is through 3rd parties that share and sell data to them and this can't be accurate, they aren't the result of analytics. So, it's just a brief estimation. If you sign in and out of the website for 10 times an hour a day, it won't count on similarweb if website's GA is not connected to them.
Which source for visitor numbers would you recommend or suggest using as a comparator for what could be deemed more accurate statistics?
There are some like semrush, ahrefs and so on but all traffic estimation tools only give you a broad guesses unless the website has google analytics script put on page and connect it to similarweb or any other traffic estimator.