That's a big Bravo Sierra!
The money that is taken from your paycheck is YOURS along with any interest/capital gains on it!!!!
That's not correct. You agreed to defer receipt of some of your compensation. If it was yours, you would have been taxed on it. You have a nonforfeitable right to the money at some time in the future, but today it's not your money.
In 1933 there some folks that thought the gold that they had bought and paid for was theirs too. SURPRIZE!