#at least in IA1 he had some depth (though his decency was lacking) but in the sequels

[lunarblue21]

Sid in IA1: has basically zero plot relevance; is disconnected or really, more unconnected from the humans (the overriding element tying everyone together) in his backstory; functions primarily as a supporting comic relief to lighten the tone of Manny and Diego's heavier backgrounded stories in the main plot, is the one character most easily subtracted from the cast if need be, because he has NO relevance to the "destruction humans cause" plots in Manny and Diego's backstories nor does he have any impact on Diego's redemption arc since Diego's heart changes because Manny saves him, making him rethink everything and because of Roshan's love towards him whilst Sid contributes basically nothing to either of those arcs that give both Manny and Diego character development as their own characters and because of their impact on each other, they help each other grow. Sid meanwhile, has no character growth/development in IA1. He ends the same character as he was in the beginning.

Sid in the sequels: shoehorned into plot relevance by basically making him into a Black Hole Sue where everything revolves around him - IA3 is an egregious example of this, the only exception is IA4, where the cast becomes sort of an "ensemble" again a la IA1 but with character development lacking, unlike IA1, where Manny and Diego have strong character development during their arcs - still has virtually zero character development despite being made a plot-driver in the sequels, has lost his function of the comic relief to support/uplift Manny and Diego's darker-toned arcs and essences as characters since he is squished into a "main character" role when Sid is best suited as a "supporting character" since his entire IA1 purpose was to provide leaven and a contrast to Manny and Diego's more sombre tones and circumstances.

Taking all of that away from him in a comedic context leaves Sid an empty vessel of a character in the sequels.