I don't believe for a second it would have been good storytelling to have Letho working against Radovid and would have been grossly out of character for Letho. I also expected Emhyr to betray Letho to be honest. I think it works very well and adds to the main story considerably to have Emhyr have betrayed Letho. It certainly influenced my decision to not turn over Ciri.
Disagreeing with the interpretation is not the same as bad writing.
As for the Scoia'tael, while it was part of the Peace Treaty, Emhyr made it clear that they weren't allowed to stop fighting either.
‘Emhyr Deithwen gave us Dol Blathanna as a gift. What do you expect from me, Filavandrel? Am I to demand more? Do not forget that even in receiving gifts there should be moderation. Particularly when it concerns gifts from Emhyr, because he gives nothing for nothing. We must keep the lands he gave us. And the powers at our disposal are barely sufficient to retain Dol Blathanna.’
‘Let us then withdraw our commandos from Temeria, Redania and Kaedwen,’ suggested the white-haired elf. ‘Let us withdraw all Scoia’tael forces who are fighting the humans. You are now queen, Enid, and they will obey your orders. Now that we have our own small scrap of land, there is no sense in their continuing to fight. Their duty is to return and defend the Valley of the Flowers. Let them fight as a free people in defence of their own borders. Right now they are falling like bandits in the forests!’
The elf bowed her head. ‘Emhyr has not permitted that,’ she whispered. ‘The commandos are to fight on.’
‘Why? To what end?’ said Filavandrel aep Fidhail,sitting up abruptly.
‘I will say more. We are not to support nor to help the Scoia’tael. This was the condition set by Foltest and Henselt. Temeria and Kaedwen will respect our rule in Dol Blathanna, but only if we officially condemn the Squirrels’ aggression and distance ourselves from them.’ ‘
Those children are dying, Daisy. They are dying every day, perishing in an unequal contest. As a direct result of these secret pacts with Emhyr, humans will attack the commandos and crush them. They are our children, our future! Our blood! And you tell me we should dissociate ourselves from them? Que’ss aen me dicette, Enid? Vorsaeke’llan? Aen vaine?’
The elf bowed her head. ‘Emhyr has not permitted that,’ she whispered. ‘The commandos are to fight on.’
‘The commandos,’ she repeated softly, ‘must continue to fight. They must disrupt the human kingdoms and hinder their preparations for war. That is the order of Emhyr and I may not oppose Emhyr. Forgive me, Filavandrel.’
Filavandrel aep Fidhail looked at her and bowed low. ‘I forgive you, Enid. But I do not know if they will.’