Re: Who uses the full BGP table
1.4 million routes doesn't really sound like much to me for 2022. Other than the big service providers who really needs to carry the full bgp table anyway? Most folks that use BGP will probably only need a tiny fraction of it, or for the rest of us just uplink to a good service provider(in my case Internap) and let them do the routing.
If you are single-homed (only one connection to the ISP), you are correct, you do not need the full BGP routing table - a default route will do.
However, many organisations wish to have resiliency/redundancy. At one level, you can have two connections into your ISP and do some mucking about to avoid needing the full BGP routing table by setting route preferences etc (bearing in mind that if you want load-sharing rather than just failover, it gets 'tricky') - and you need cooperation from the ISP. If, however you want independent routes to separate ISPs you need to use the full BGP routing tables approach with some very capable routers on your autonomous system (AS) boundary to the multiple ISPs you are connecting to. It's very easy to get wrong. Once your organisation gets big enough to want multiple connections from multiple autonomous systems spread across the globe, you might want to start dealing with Route Reflectors and other techniques used to make managing multiple entry/exit points manageable rather than polynomially hard.
IP routing, at scale, is an amazing piece of co-operative software and protocol engineering which requires expertise to understand. I take my hat off to the folks who do, and listen seriously to the ones who can give reasons behind the design decisions in IPv6. It's an example of where listening to your technical experts is worthwhile, because the alternative is chaos.