all companion AI's we've seen have been small chassis
They've been in small chassis. The body is not the AI...or is it? There's an interesting question. Is Winslow the same AI in a different body, or does the new body change who he fundamentally is?
It changes everything about him; who he is, his purpose in life, how he can achieve that purpose.
It changes the fundamental relationship between him and Hanners and others around him.
Before, Winslow was a companion for a deeply troubled woman who couldn't handle many types of interaction. However over time, Hanners has worked on many of her issues. She's not "cured", but she is in a far better place than she was post her first appearance.
A companion AI feels like a stopgap fix to a deeper personal problem, to be someone to provide companionship to a human while also subtly working to help develop someone's interpersonal skills. Likewise, the AI is in a caring environment which allows themselves to develop. Pintsize works as something of a troll, to provoke Marten into developing past the milquetoast personality he had at the beginning of the comic. Momo worked to remind Marigold to get away from the computer and not to surrender to the hikikomori lifestyle. She still provides companionship through being a roommate, ensuring that Marigold wasn't lonely when Angus left. Both AI have grown in response to their relationships to their respective human friends.
But what about Winslow? In the case of Pintsize and Momo, outside influences helped their humans develop but in such a way that the respective AI were still an integral part of their lives. Pintsize is a troll and a disgusting one at that, but at the same time, he serves as an outlet for some of the issues Marten and Faye possess and as something of the gadfly. Momo still provides companionship for Marigold, as a best friend and as a roommate while at the same time, allows Momo to stand on her own two feet with a great deal of independence. But Winslow? Can we really say that Winslow has grown since his first appearance? Hanners has, in how she interacts with people and lives her life. When she became a main character first, there was no way that Hanners would go into the basement of Coffee of Doom to roast coffee. Now look at her. But Winslow feels like he's been left behind in the dust when it comes to social interaction and knowing what he wants.
Its too much too soon for a little AI who isn't ready for the change in dynamic.