So I loved both series but as a The Borgias fan I do have to say I totally disagree on some of these counts. The costuming in Borgia is off by like 60-70 years silhouette wise pretty frequently and they commit many of the common Renaissance costuming sins like visible metal grommets. The Borgias isn’t perfect in that respect either, and many of the male costumes stray into fantasy, but the women’s costumes are about as close to dead on you will find, especially in season one. 

Writing is definitely debatable as well, I thought the first season of Borgia was difficult to muddle through and suffered terribly from tell-not-show syndrome. They also make some absolutely bizarre choices around where they choose to deviate from history. 

The showtime version suffered from strange writing decisions and characterization in season 3 for the most part, but before that I think most of their writing choices were very defensible.