Actually you can launch it to the addons screen, though that is rather hit or miss after an update.
It is a replacement for the previous curse client, which will in time be phased out.
So if you used the previous client, then that isn't additional but intended in time to be a replacement.
For me the splash screen duration isn't too different from the previous list of steps, though arguably if it is just for animation purposes an option to skip it would be nice.
I agree that it doesn't do everything right, but then no program by a 3rd party will tend to.
Curse make money off those extra services, so it makes sense to have them up front and center in the client if people do use them.
Those that don't want an individual client, those that do may well benefit from them together.
You can't please everyone.