The really impressive thing about Valve is the amount of revenue they make with a relatively small head count. They have about 1/10 the number of employees as EA.
Seems about right. They don't have a complete monopoly and the industry seems to be making most of their money off micro-transactions these days instead of sales, something valve takes no cut of outside there own games. Meanwhile apple and google do have monopolies and take a cut of micro-transactions which accounts for there significantly larger revenue.
But how could Valve have made $6.5b off of their own games? They haven't released anything in yonks have they?! Plus EA have the gacha-fication of FIFA/every other sports game franchise they own with Ultimate Team, etc.