Which is why the sufficient numbers I referenced to threaten the Faith with was the Tyrell army of around 15,000 Randal Tarley brought to release Margeary, and assumed it would take a similar number if Cersei wanted to get out, which the Lannisters should theoretically still have had. As for the Freys, I understand that but you have to admit this is still stretching their forces pretty thin given the number of commitments they have.

I wouldn’t necessarily make that assumption; Tarly brought the force he had on hand, and he’s not averse to over-doing it to win through overawing them vs. a heads-up fight. 

And yes, they’re stretched thin. That’s kind of the whole point of the Frey and Lannister plot in AFFC/ADWD, that they’ve succumbed to victory disease and are massively overreaching themselves, which will bring about their downfall. 

Take House Frey for example – they’ve only got 4,000 men and they’re trying to take over the North and the Riverlands. They’ve got men at Darry, Seagard, Riverrun, and Winterfell trying to hold it all, but they’re starting to die like flies. Doom is upon them.