Yep, Twitch's Flash player is the culprit, but Twitch is not owning up to the problem and, in many cases, blaming ISPs for slow performance. Twitch staff members' comments are all over Reddit (among other social networking platforms) and insist that Twitch, its Flash player or internal network is not to blame.
And that's where I discovered that viewers can bypass Twitch's buggy Flash player by using 3rd party programs that utilize Twitch's HTTP Live Streaming (or HLS) protocol. Unfortunately, only Safari for Mac/iOS, the stock browser for Android, and Chrome for Android have HLS protocol support built in (the Edge Browser for Windows 10 will have HLS support but of course not everyone has Windows 10 yet). However, for Windows systems, we could use LiveStreamer, or the one I use now, Tardsplaya.
I also read that Twitch is already working on their HTML5 player, and they already have a functional prototype, but it is understandably far from deployment. By the way, HLS is different from HTML5. Twitch says that HLS is merely a "hack for several platforms", and they are moving towards providing a full HTML5 player "soon".
So, there you go. For everyone's guidance.
Thanks for the updates Bro, your contribution to the community certainly benefits many users.