>>11547424
>>11547459
If you want something more simple, you could always just disregard all the lore and just treat Eternia playset as the toy version of Palace Eternia that Randor rules the planet from

It's not like playsets actually looked like their toon counterparts anyway.
And if you need to explain Grayskull Tower and Viper Tower, just chalk them up to "design shorthand" for Randor having a monorail to quickly get warriors from the palace to Grayskull to defend it or to Snake Mountain to attack it