@ square root of 2
“An underlying difficulty I have is that if the mesillas yesharim is correct, then why is the world so prone to bad and not good? If the entire point is to get sechar, why is it that “noach lo leadam shelo nivra”–why did Hashem not make it that it would be easier to get gan eden than gehenom?”
This is an excellent question. So excellent in fact that the RAMCHAL made it the primary subject of a whole sefer which he wrote called Daat Tvunos.
“Why is it that those who get saved from gehenom are one in many, and those that make it to gan eden are the minority”
As someone already pointed out above getting saved from gehenom is one thing making it to Olam Haba is another.