As long as both your TV and the AVR support eARC, that's exactly how it's supposed to work.
It's all down to the individual speakers, and what sounds best to you. But generally, towers being larger can fit larger speakers than bookshelves. Towers typically come as either two or three-way. In two ways you have a tweeter and woofer, while three ways have a driver as well to better handle mids.
Audio comes down to personal preference, and size, shape, and things in a room can affect the sound. I used to have a nice 7.1 system with a projector, nowadays I just have sound bars. I don't even hit 25% on the volume before it gets uncomfortably loud.
If I were getting something new right now, unless I needed it immediately, wait for Black Friday sales unless you see some crazy deal by you. You could get a full sound bar system with a sub and two rear speakers for $300-400. When looking at new AVRs the prices just skyrocketed and no one is making the entry/mid-level systems anymore as everyone now just gets a soundbars.
Audio is always tricky, but if you're not an audiophile, the vast amount of people would find even a budget entry-level soundbar to meet their needs. But there's no way for you to know what should right to you with hearing systems, so hopefully some place by you has some demo setups.