Senior SWE salaries I'm finding in a quick google search in Spain are 80k eur. According to levels.fyi [1] Google (and presumably the other clouds) are paying 170k eur. The comparison isn't even "is 4x the salary better in the US?" it's "is 2x the salary better in the same place?" which is obviously yes.
[1] https://www.levels.fyi/companies/google/salaries/software-en...