It applies the same philosophy but doesn't require special data types. Not all data stores support decimal numbers, and every programming language I've used uses floating point numbers my default. JS doesn't seem to even have a native decimal implementation at all.

Strings work everywhere, and are first-class data types it most systems/languages. They take more bits per digit than numbers (though you can choose a wider alphabet to mitigate that, such as ASCII 33 '!' through 126 '~'), but I'm happy to trade the storage away for using a first-class data types.

Floating point numbers aren't special data types either.

You don't need decimal. It works fine with binary floating point. The reason they don't call it robust is that it requires re-balancing, but so does your proposal.

float/double data types have a hard requirement of periodic rebalancing to support unbounded repositions. Lexicographical sorting does not require rebalancing ever, though it may be performed as an optional storage/bandwidth optimization. That is a very meaningful distinction in my book.

I would use byte array instead of strings, as they should be supported by everything and they are more compact. But I'm crazy guy who wants to optimize everything, I think that in reality string will work just as well and probably easier to debug when you need to deal with it (also easier to serialize if you need to pass it around).

What makes you say it's less efficient? It's exactly analogous to storing increasing decimal values between 0 and 1, just using base 26 digits (encoded A-Z) rather than base 10 or base 2.

Start with .M (encoded as "M"); add in .F, .T to insert before or after. Once you find yourself trying to insert between .M and .N, do it by adding .MM.

But in a database char types can be arbitrarily long, and database indexes are well suited to indexing them. That gives them a lot of advantages for this kind of usecase.

Since your alphabet is composed of 8-bit words, you'd get more mileage out of each byte by using 256 symbols in your alphabet, one for each binary value. And by using binary as your alphabet makes things conceptually simpler (even if the values are stored as 8-bit words).