I am actually not really sure if those people really believe that IPv6 will EVER replace IPv4, which in my opinion will never happen.
Can you elaborate? IPv6's share of traffic has been increasing at about 0.5% per month for the past year. If IPv4 has 80% and IPv6 20% this month, next month it'll be 79.5 vs 20.5. So in your opinion... what? The change will stop? When? Why?
Everyone is able to sign up with RIPE and get a /22, thats around 1000 IP addresses. For years the RIRs want to tell us that IP addresses run out but I am still able, today, to pay some bucks and get IPv4 addresses without issues. The issue was that exactly those RIRs handed out IPv4 addresses years ago like there is no tomorrow and now they want us to switch to a broken protocol because they made a huge mistake. I won't deny that we are months (around 2 years) away from the RIPE actually running out of IPs.
Part of my job leasing out IPv4 space is also monitoring different sources, like Spamhaus, if my client or client of clients send spam with my IPs. What I can tell you is that with IPv4 already this is messy but if I think about IPv6 this is impossible to track or control and a complete nightmare. Also, for example if you operate a mail server that only runs IPv6 and send emails to gmail they will outright block you or just send it to the spam folder. Please note that this is only one of many examples.
Apart from that, if I look at the implementation of cloud providers like DO, Linode, OVH, Scaleway, etc. this is all a big joke. Also, IPv6 routes from some tier 1 upstream to others are down for days without anyone noticing it, because most people want IPv6, but no one is actually using it. It's like having a todo list and IPv6 is done but how it's been implemented doesn't matter at all.
You should also be careful with statistics, as a lot of scammers switched to IPv6 so I would not be surprised if a lot of the "IPv6 market share" is from scammers.