Oh gods, this is hilarious. Unintentionally, of course, but still.
Let's go down your fun little list one by one, as far as it is worth it to go.
- DT_RPATH does exist. It is the name of the ELF dynamic tag that is used to implement various linkers' RPATH flags. (It sucks because it wires paths into binaries in a way that is impossible to override without binary editing: DT_RUNPATH sucks slightly less, but still wires paths into binaries, which is less than good).
- The glibc runtime linker was rewritten from scratch for ELF support. It doesn't support a.out, and never has. Linker caching exists because it provides a huge speedup over searching at runtime; its search path exists to allow that to be customized; and RUNPATH is a mild abomination, as you would immediately realize if you had ever had a binary with a runpath that had a path baked into it (often a build path) which was pointing to an NFS server that had become unavailable. I've used Solaris for many, many years, and believe me the number of bugs we had reported that were attributable to mis-set LD_LIBRARY_PATHs (which were *all supposed to have the same value* and which on Linux would just have been set in /etc/ld.so.conf) was simply astonishing.
The rest of your comment is as far as I can tell pure ad hominems, arguments from authority, and straw man attacks, not worthy of a response. ("based on outdated technologies from the 1970s", I'll bet if I ask the actual authors, the only people who might know, they would disagree.)