Hello Brian
Yes, I understand your concern. After spending years (and some of us decades) learning and understanding IPv4 with both its strengths and its limitations, it is very often hard to avoid viewing IPv6 in a similar manner.
Now if you have a prefix length of 48, 64 or even 96 bits which are all very common in IPv6, then of course you will have a subnet capable of supporting an ridiculously enormous number of hosts. Although IPv6 can actually handle a greater number of hosts per subnet than IPv4 (because there are no broadcasts and because it handles addressing differently) it would not be wise to actually use all those addresses.
With IPv4, in order to conserve addresses, we subnetted our scopes to sizes comparable to what we need. With IPv6 you don’t need to do that because there are just so many addresses available there is no concern for address exhaustion. So, in order to simplify addressing, just make all your subnets with a /64 prefix and be done with it. Just don’t actually physically place more than 500 devices within a subnet.
I hope this has been helpful!
Laz