You asked if anyone has transitioned from syrup-sweet to unsweetened... so I am chiming in, as that is exactly what I did.
Background for me is that I came from a long history of drinking lots of very sweet drinks, primarily Coke and southern sweet tea. I made a good strong pitcher of sweet black tea with 2 (yes, I know) cups of white sugar per gallon. I was drinking 3 to 4 quarts of this stuff every day! Over a year or so, I'd gained about 10 pounds I wanted to take off, so I targeted the sugar in my tea as a way to eliminate a considerable amount of daily calories. I switched to artificial sweeteners... never developed a taste for Splenda, and couldn't get the right sweet taste for a while, but after experimenting, I finally arrived on a mixture of 2 packets Equal and 1 packet Sweet and Low per about 32 oz. of tea. Reallllly sweet. Makes me shudder now to think of it.
I got off the artificial sweeteners around the same time that I really started exploring loose tea... coinciding with my discovering Adagio and TeaChat. My reasons for stopping these sweeteners were several... first, I had a weird medical episode that we couldn't figure out for the longest time, and after tons of research on everything from vitamin deficiencies to poisons to tick bites to artificial sweeteners... I didn't like what I learned about Equal and Sweet and Low. I was partially worried about health concerns, and I was partially stunned to learn about the weight-gain implications for people who use lots of artificial sweeteners. Since weight control was my main reason for using them, and since I didn't notice any substantial weight loss when I switched from sugar, and since evidence suggests that artificial sweeteners may stimulate carb cravings... well, anyway, I knew I wanted them out of my diet.
It was good timing for me, because I'd ordered a ton of samples from Adagio, and I was learning from members here about the different characteristics in tea flavors, all of which I had been masking with sugar or sweeteners, to the point that assam tasted the same as ceylon to me. When I started tasting them unsweetened, it was like having a whole new beverage with nuances I'd never even imagined. I also lost about 8 lbs.
That being said... I still sweeten iced tea sometimes... but only lightly, and only with sugar, no more artificial sweeteners for me these days. I don't sweeten hot tea at all, except for occasional chai blends. So that's my "why and how" story.