as shown in the beginning of homestuck a single layer of prototyping results in a still useless sprite, so why is tavrosprite not like this, is it because he is a sentient being? this would explain becsprite and also applies to rosesprite

It may be because he’s a sentient creature. Becquerel is sentient and so is Rose so that may be why they’re a full sprite and not a floating circle. The harlequin doll and the crow Dave accidentally prototyped were also both prototyped pre-entry so that may be why they were a floating circle for a while.