Couple of problems.
Mara Sov did not release Skolas. Xur did, by the order of the Nine.
Secondly, the Queen (IF she was Savathun), is not in her Throne World, as Uldren can feel Mara's pull.
English
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Mara sent Skolas to them as a gift. You think the master of manipulation had no idea what they'd do? Oryx felt the loss of Crota in his throne world. It's not a leap to think Savathun could influence her servants from hers.
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Oryx felt the loss of Crota because his tribute stopped flowing. His absence quite literally felt an overwhelming hunger to Oryx.