I just learned that the senior in my team earns more after taxes than my gross salary (medior) per month :(

While he is a full remote worker from a country where the average salary is 60% of my countries average salary.

While i'm certainly happy for his salary... My salary does not look correct compared to his

There is only one question are you happy with your salary?

There should never be the question, blabla earns X are you still happy with your salary.

Obviously it's great to talk about salaries and such to get a feeling for your salary and if it feels way off then obviously you have to ask for a raise.

If you ask for a raise prepare good reasons what you did great for the company. How your responsibilities have increased and so on.
Senior gets 3x the money I get and he sucks is not a good argument for a raise. In a discussion about your salary should never come up the salary of any other person.

We often forget to do the maths on how much an annual % raise can amount to

If you earn 70K and get a 5% raise you'll end up with 114K after ten years

This is a blessing and a curse - people talk about expecting a % increase but they kinda forget that the amount per year becomes HUGE

And then we have the situation where some people were hired during eras where it was hard to hire and the company was desperate to start new projects so they overpaid new hires and then lowered starting salaries other years