Earlier quoted context omitted.
Steam does have a very slow boot time, but the expected behavior is that Steam is always running in the background so I can't imagine it's a priority. I can't fathom a ~3 second wait when installing and launching a game being a real problem. Minor annoyance sure but that's less time than you'll be forced to see stupid splash screens for!
I just quit Steam (so it was fresh in cache, never mind relying on SSD etc.), and started a Steam game. It took 20 seconds before the game launched (not playable, just started). That's massive. Pretty much any of my non-steam games will be launched and playable within 10 seconds. (I also hate unskippable intro videos; I'm fairly sure I've collectively spent much longer searching for ways to delete / skip such videos…
For all my Source games: "-novid -w 1920 -h 1080 -window -noborder"