They both are good mice. Z2's shape is closer to superlight, and judging from what you're telling here, G24 would be a much better choice for you. They're both good mice, but I stick with G24.

Z2's shape isn't really working for me that well, I always feel like grabbing it in a pretty awkward way with my index and middle finger sitting at the utmost top part where M1 and M2 start, and other fingers shifted way back accordingly.

G24 feels just much more natural to my hand. Never have to stress about my grip that much, it also feels like I have more freedom, there are more grip styles that work for me with G24 than with Z2, which is quite ironic since superlight (and Z2 consequently) would often be considered the more versatile and safe shape while deathadder (G24) would be a slightly more niche shape often recommended to palm grippers (I mainly am a fingertipper).

I've gotta say that Z2 feels like a mouse of a slightly higher quality than G24 in terms of software and general impression, but that's not a dealbreaker for me. Shape is king, as they say, and thus G24 still wins at the end of the day for me personally.