Are RouterOS commands written in a scripting language or hardcoded into the CLI?
If scripted, are they changeable? For example, I’d prefer that /interface/w60g/monitor display the values horizontally.
How do I retrieve the MCS, RSSI and SIGNAL values without using monitor?
You cannot control the output format of commands, but of course you can write scripts that call commands and do something to display the results.
You can do that on the router itself (/system script) or you can wite scripts on other computers that use API to retrieve values and display them in the format you like, possibly after gathering info from multiple places and combining them.
There are some API libraries for languages like Perl and PHP that you can use so you can avoid starting from scratch.