I have one and use it for gaming across PS4, Xbox One and Switch. The picture is superb, and although the response (22ms) is well below what the LG sets are capable of (13ms), it's not something anyone but the most hardcore twitch gamers would notice. For example, I play CoD casually on mine most days and it feels totally responsive.
In real world terms, how important HDMI 2.1 will be in the next few years is a bit up in the air at the moment in my opinion. I was between the GZ950 and the C9, and eventually chose the GZ950 as it was reputed to have better out of the box calibration and accuracy (especially important to me as I will not be getting a pro calibration). It also didn't have that annoying looking Wiimote style remote. I accepted the lack of HDMI 2.1 as the trade-off for this.
This is because, while I do play a fair number of games, I'm not totally convinced HDMI 2.1 is going to be a big deal for a while yet. The main things that it offers are higher framerates (up to 120fps over 4K), and VRR.
In the case of the former, this will apply to an incredibly tiny percentage of games on PS5 and XSX. My guess is you will probably be able to count them on one hand. Most games will probably target 30fps, with a few hitting 60, and a very very small number rising above that. That's because 120fps will eat an insane amount of compute power, and will only benefit the comparatively tiny number of people who have HDMI 2.1 TVs.
VRR is the feature that is much more likely to be practically useful on a day to day level. But I question the current implementation of this - on the latest LG sets, it still only supports a narrow range of framerates between about 45 and 60 fps (might have that slightly wrong but it's around there). Anything below that, you won't get the effect of VRR. Most games are below that.
We've also already got VRR implemented on the current Xbox One X, but based on anecdotal reports online and from people I know with compatible HDMI 2.1 TVs, it really doesn't seem like it's making a whole lot of difference at the moment.
In my humble opinion, the real benefits of VRR will kick in in a few years time, once TVs support a much wider range of framerates for it, and more HDMI 2.1 TVs are in homes. This will incentivise more developers to make use of it, and to make better use of it.
With all that in mind, it didn't seem worth it to me to take a potential trade-off in accuracy and out-of-the-box calibration (which will affect everything I look at on the screen), for the currently slightly nebulous benefits of HDMI 2.1 (which will only affect certain games).
That was my rationale for selecting the GZ950, and I hope it helps you