How much of a contributing factor to ranking is it really?
Page speed matters and a lot, not just to improve your site´s organic rankings but, also, when it comes to improving your site´s conversion rate.
Page speed is strongly related to offering your visitors with a better user-experience (UX) and this is something Google cares about a lot. So, saying page loading speed doesn´t matter is just BS.
There are exceptions to this rule of course. If you´re already an authority on your industry/niche, Google won´t care too much if your site loads in 10secs for example.
But, if you´re launching a brand new site on a brand new domain and would like to rank high on the SERP you better heavily focus on offering your visitors with the best possible UX you can and that includes page speed.
Let me ask you this...When was the last time you waited more than 5 seconds for a website to load on your phone?
Now imagine having an e-commerce website with a product page taking 5+ seconds to load...Will you have the patience to complete the checkout process? - I don´t think so.
Personally, I think whether or not is a ranking factor it´s secondary to the main fact that page loading speed affects your site´s conversion rate and the UX, and this is more than enough for me to take notice and work on this.
Cheers and stay safe!