No, you don't have to use conditionals.
paracol has the option/command
\twosided for that, which, according to what is written in the manual in p. 18 supersedes
\swapcolumninevenpages (which is how I found this command, i.e. even though
\swapcolumninevenpages is lengthy it describes more clearly what this does). This is illustrated in the following MWE where the Y column is left/right depending on whether the page number is even/odd.