Honestly, I find the bardcore version to be less good than the original. It misses this specific thing I can't point a finger at yet, I need to think about it.
Speaking for myself, it's a matter of *bombast* (bombad bombast, one might even say
).
The Imperial March, even to a non-music-nerd person like me who can barely describe her own feelings on why she likes a piece of music, is awe-inspiring and dramatic because of the bombast and authority invoked by it being, well, an orchestral march that has numerous violins, trumpets, and other instruments working in symphony. And to an extent, the out-of-universe knowledge that it's the theme for the galaxy-dominating Empire--an Empire that demands all this synchronization and conformity and forced unity in its population--factors into that music itself as a theme of that empire.
Simplifying a work down to an essential tune using limited instrumentation as the medieval stuff does can work and be a neat twist on something. In some cases it can carry the 'theme' of the work and removing the flourishes makes it more interesting itself (personally, I think it's the case with a lot of the pop songs that get the treatment--and you see something of a corollary in the
Cantina song, for instance*). But you're going to encounter trouble when you try to pull that simplification trick on a piece of music that is built around being complex and symphonic as part of its very
theme that it was written around.
*Or, as another comparison, the
Duel of the Fates. Which, to me, still 'works' in the different style. It doesn't lose the grandness or theme that is central to it--it's just reoriented to a different sound.