I think a better question is how has yoyo design evolved rather than just shape, so I’ll cover that.
Responsive yoyos were common place in the 90s, people started experimenting with unresponsive and binding around this time but nobody was really doing full unresponsive play. The 90s saw a shift from very narrow to slightly more wider yoyos (still pretty narrow by today’s standards though). Early 2000s players started experimenting more with semi-responsive and unresponsive play but it wasn’t really the norm until Johnnie Delvalle’s iconic 2003 Worlds performance. After that, more people started to switch to unresponsive play and the Hitman that was used became a huge hit.
The few years following that, you could see bigger and wider yoyos became a little more common, walls became a little lower, and silicone/response pads started becoming more common. Undersized, mid-high walled, and narrow yoyos were still being released very frequently around this time though so the general consensus hadn’t completely switched to “bigger and wider is better” quite yet.
In the late 2000s, a few companies started to experiment with 7075 aluminum, which was stronger than the commonly used 6061 aluminum. Bigger, wider, lower walls became more and more relevant but a complete shift hadn’t happened quite yet. Silicone/response pads were pretty much used and seen as the superior response by everyone by this point.
In the early 2010s, companies started to experiment with bimetals as we know them today. Then, in 2013, we pretty much hit the “peak” of yoyo design with the Draupnir. Around that same time, 2013-2014, was when undersized and narrow really became seen as obsolete and fewer and fewer companies were making them, especially with a competitive mindset. Since 2014, yoyo design hasn’t exactly “advanced” but 7075/68, titanium, and bimetals started to be much more commonplace and yoyos have just gradually gotten better and cheaper overall to the point where almost everything you buy now is a good yoyo. Something that couldn’t really be said in the 2000s or even early 2010s.
I think each of these time periods had a yoyo that changed the game as we knew it. First it was the Duncan Freehand in like 2000, which was seen as very wide when it was first released. Then it was the Hitman in 2003, it changed how we view unresponsive play. Next was the Peak, 2006, it was bigger, wider, and walls were a little lower. In 2009, the Sleipnir was released. This was basically the final progression in monometal design. Angular shape, full sized, wide, low-walled, 7075. Lastly, was the Draupnir in 2013, basically the pinnacle of bimetal design. Then there’s today. Although there may have been a few yoyos that have been released that are arguably better than the Draupnir, there hasn’t been a yoyo that trumps it by so much that it becomes a game changer like the Hitman or the Sleipnir.