Arduino VS Stand-alone Microcontroller for a Beginner
I'm currently in my second year of studies at a public university in the US.
I started out on the Arduino on my own in high school, although my later classes (my intro embedded class) used a TI MSP430.

The Arduino has the benefit of being well supported by hobbyists with good tutorials for beginners, but as it seems, won't really earn you the respect of a "true embedded systems" developer, as far as I can tell, more or less what you gather.

If you're looking for a gentle introduction to embedded systems, I would say the Arduino is the way to go. Otherwise, as you have mentioned, there's plenty of other places to go, and frankly the Arduino often is not the best choice when considering hobbyist projects. In that case, I'd think a chip like the MSP430 (the value line development board) is a cheap and effective way to learn about microcontrollers, likely giving you more options, at the cost of a steeper learning curve.

In any case, as there are many microcontroller development boards today, perhaps it is more important that you gain experience with one system, and then broaden your knowledge to be able to handle things more generally. Jumping in and getting your feet wet is probably more important than finding a specific chip, since you aren't exactly trying to design a product with a specific application in mind - you are simply learning about microcontrollers.