To start with it requires support v4 as a separate network, at least for internal networks, since many devices don't support ipv6 (I have several AP's, IoT devices,etc.. bought in recent years that are like that). Then the v4->v6 nat/gateway/proxy approaches don't work well for cases where reliability and performance are critical. You mentioned NAT, but lack of NAT means you have to configure firewall rules, many get a public ip by their ISP directly to the first device that connects to the ISP modem,exposing their device directly to the internet. Others need to do expose a lan service on devices (port forwarding) which is more painful with v6. DHCP works very simply, v6 addressing can be made simply too (especially with the v4 patterned addressing - forgot its name) but you have multiple types of v6 addresses, the only way to easily access resources with v6 is to use host names. with v4 you can just type an IP easily and access a resource. Same with troubleshooting, it's more painful because it is more complex, and it requires more learning by users, and if you have dual stack, that doesn't add to the management/admin burden, it multiplies it. It's easier to tcpdump and troubleshoot arp, dhcp and routing with v4 than it is ND,RA,anycast,linklocal,etc.. with v6.

For mobile connectivity, ipv4 works smoothly as well in my experience, but I don't know about your use case to form an opinion. I don't doubt IPv6 makes some things much easier to solve than ipv4. I am also not dismissing IPv6 as a pointless protocol, it does indeed solve lots of problems, but the problem it solves is largely for network administrators, even then you won't find a private network in a cloud provider with v6, for good reason too.