You definitely don’t need a streamer to get absolutely top notch performance. You may like the streamer better subjectively, but objectively there’s nothing particularly better about it. If it’s functionality works out better for you then go for it. If you think it sounds better, go for it. If you haven’t tried a streamer yet, I think it’d be best to find out as much as possible before committing.
A music streamer is a lot like a game console. Hardly anybody will say that a game console can play games better than a computer. Quite the opposite. However, a game console has a lot of conveniences and plays games well enough for most everybody. For me, a console is overall a better experience for gaming. For music playback, I’ve found I prefer the computer over dedicated streamers. It has to do with how I listen. If you want the absolute best performance and flexibility use a computer. If you want a walled garden experience that will sound good enough, maybe even better to some subjectively, get a streamer.
Some things I’ll confess I don’t like about the computer:
1. It’s complicated, with a lot of settings. I can lose track of what all is going on.
2. It’s a multipurpose machine and may interrupt your music session with other business.
3. A software update can create some havoc now and then.
Having said all that, I’ve had streaming devices produce similar issues now and then. I’ve not tried them all, but I’ve read reports of similar issues with even very well regarded high end streamers, so as someone said earlier, it’s still a computer and will still have some of these issues.
Actually, I should clarify that I still do use a streaming device, but the computer is also hooked up and I find myself gravitating mostly toward it as the primary streaming source.
Directly responding to the original question of ethernet for sound quality, you'll have to decide for yourself. There is no consensus on a broad scale, and certainly no repeatable testing that has shown conclusively that there's a lot going on with sound quality concerning your ethernet connection. You can gather opinions here so I'll give you mine - it hardly matters. Your speakers and room, no matter how good, are going to be veiling the sound by orders of magnitude more than your ethernet connection or choice of streamer. I won't say that you or someone else can't hear it. But I wouldn't let anyone else tell you what to expect. You'll have to listen for yourself and decide what matters to you.
