Why? Sending a message to a Google Voice number will always happen over SMS or MMS. iMessage does not work over GV. RCS does not work over GV. If you mean try receiving messages from an AT&T Android phone, sure, I've done that. No complaints, although AT&T seems to throttle the image size more than other carriers in my experience.
By your experience it seems that Apple is limiting iOS-iOS image size, to promote iMessage
What? If I were sending messages to an iOS device directly it would go out over iMessage. Instead I chose to send a message via MMS to a Google Voice number where Google serves as the end device. iMessage does not work over Google Voice. There. Is. No. 200. Kilobyte. Limit. There's no gatekeeping, just shitty carrier MMS implementations.
