I agree. I programmed a few internal LaTeX "packages" for my department in the university. I not only typed some math, it includes a lot of strange macros.

The "programming language" is horrible. It's a clear example of a turing tarpit. For example you don't have arrays, so you must fake them. You don't have function, so you have to return the value in a glob@l. Monkey patching is considered an art, but this makes many of the different packages slightly incompatible.

The "printing library" is amazing. If you only want to do a standard thing (and someone else had programmed it) the result is nice.

The other advantage is that everyone knows it, so if you make a package correctly it is easy to use by mathematicians that can't program in LaTeX.

Yes, the TeX language is pretty horrible (indeed, the whole concept of TeX is a testament to the strength of cannabis available in the Bay Area in the 70s - it's not a typesetting system, it's two separate programming languages which typeset as a side effect!). LuaTeX is an attempt to remedy this situation by embedding lua in the TeX engine: http://www.luatex.org/

(It's also no coincidence that the development of BibTeX coincides with the crack epidemic, but I digress.)

The syntax for optional argument and the lack of support of named parameters are limitations of LaTeX, not TeX. For example, see ConTeXt, which is a macro package on top of TeX, that has much more consistent syntax and all macros accept named arguments.

TeX (PlainTeX) doesn't have support for optional arguments or named parameters (perhaps in some primitives, but they are very different of the optional arguments in LaTeX).

But TeX has a extremely flexible macro system, so it is possible to fake optional arguments. That's what LaTeX do. LaTeX defines a standard way to have optional parameters and make easy to define and use them. It has some strange optional parameters like in \newtheorem, because they are really fake optional parameters. The starred versions of the command also are fake, and have to be defined using a trick. But if you are lucky and don't look under the hood everything works quite well.

I don't know enough about ConTeXt, but I hope that it has a better system for optional arguments.

In some way, this is similar to what happens with some features of high level languages and assembler. For example, the exceptions in C# or Java are translated sooner or later to assembler, but assembler doesn't have exceptions.