PEP 703 isn’t about a feature that was already merged and in released Python versions, so it’s hardly a reasonable comparison 
Yes, ideally it would be sent to the SC before that six month deadline with enough time for the SC to decide, but that’s mostly because we want a clear decision from the community, and we don’t want a lackluster discussion with no community engagement that’s then written up in a PEP and sent to the SC to check off requirements on a list.
This is a significant change that requires serious attention. If we can’t get a clear decision in six months time, something that’s compelling enough that the SC doesn’t have to create a five year plan just to make it acceptable to the community, then we need to rethink how we approach the JIT. That doesn’t necessarily mean the JIT immediately gets ripped out when that six month deadline is hit – we’re not unreasonable – but we do want this to be taken seriously.