Yeah, I hate to be that guy that claims that Trish and Koichi are similar because their Stands talk, but I just want to share an observation.
DISCLAIMER: This is all conjecture, I'm just one of those people who loves to piece the lore together.
Firstly, Koichi wasn't supposed to have a Stand, Josuke kinda cheated it in for him. And even then, Koichi's spirit wasn't that strong, so it stayed as an egg. He did grow since then (just not in height), and so Echoes evolved into something useful. Act 3 is the final form of Echoes we see, it has its own personality, which is rather brash, and can act independently when its user is too busy panicking.
Nextly, Trish. While Koichi's Stand was forced onto him via the arrow, hers is inherited. If it wasn't for this adventure, it is likely Trish wouldn't have awakened it properly, or maybe it would take her a longer time (she did display some fighting spirit back when she was introduced). Anyway, as Spice Girl explains in this chapter, she awakened because Trish's spirit grew stronger. But since Trish is too busy panicking over suddenly gaining a Stand, Spice Girl acts independently, and has her own share of swears to throw at the enemy, which made me think of Echoes.
So, what I'm thinking is, when a Stand has a personality of its own, and seems more aggressive than its host, maybe it's because the host's spirit isn't strong enough to completely control the Stand? When the host lacks a fighting spirit completely, the Stand just slowly kills them, as seen (and barely averted) with Holly Kujo. But when the host has a fighting spirit, but it's just lacking, or they can still grow, the Stand can manifest without killing the host, but acts on its own.
I watched the anime past this point, and Spice Girl loses her personality after this arc and acts like an ordinary Stand. I suppose it's because Trish gained enough determination from winning her first Stand battle to bring Spice Girl under her control.
And at the end of Part 5, GER acts independently of its host, and even outright says that Giorno isn't aware of what it does, which I think means that it's become too strong for Giorno to control.