Not necessarily true, Mordred Hood was a DL character that survived the wave to become a Egg Boss. Sure Shards Metal Sonic character and Matilda's original conception (as a sister for Mighty) were done by other writers the actual creation of the two was 100% Flynn's work.
Currently these two are stuck in the limbo where we don't know what's happening with them and the new Sega mandates don't help. One mandate prevents comic only family for official Sega character but since Sega has not done squat with Mighty there's a chance they won't care. Another prevents the existence of more than one Metal Sonic but given Captain Metal's existence that rule can easily be broken.
Either way I second your last notion. Curse you Penders.

Some days, it's hard to feel mighty.