Hi @almostravioli and thanks again for pointing out the apparent discrepancy in our various documentation! I run the Support team at Netlify and wanted to make sure you knew that our leadership did discuss your feedback in detail.
As far as immediate repairs, I’ve updated our support guide to be as clear as I can about the “3Gb guaranteed, up to 6Gb occasionally possible do not rely on this please or you will be sad”. I think the pricing page is still true - sometimes you get up to 6Gb - so I have not requested that our marketing team update it, though they may choose to do so as we’ve discussed the situation with them deeply based on your feedback.
To answer your most recent question, yes, there is no memory increase for builds unless/until you are on the Enterprise plan and you purchase our High-Performance Builds add-on for that plan; in that case you do get 36Gb/8cpu’s guaranteed for each build. What we can change at any plan level Pro or above, is the amount of time available for your build before we assume it got stuck and end it for you, in case your build works well but somewhat slowly, in the smaller build environment.