While originally designed as a bolt on system to DnD, the Rolemaster “Laws” were always unwieldy to adapt to a d20 system. That didn’t matter for long, as the full suite of rules were published in fairly short order: Rolemaster was a standalone system.
Unfortunately from there, Rolemaster became ‘bipolar’: it contained quite a bit of DnD DNA but tried to establish an RM specific setting with the Loremaster line of products. (Iron Wind, Cloudlords, Vog Mur). Rolemaster was torn between the path forward in the gritty world of the Iron Wind or the well established cartoonish tropes of DnD. And soon after that, ICE rolled out the Middle Earth setting, although there is general agreement that the first few ME books (Court of Ardor & Umbar specifically) had more the feel of the Loremaster world than Middle Earth.