Dak always excels on deep throws when he has 2 good weapons at wide receiver. Look at 2019 when he had Amari Cooper and young Michael Gallup (before CeeDee was drafted). That was Dak's best throwing season (4,902 passing yards) and he excelled on his deep throws.
Dak should be able to get back to completing good deep throws now that he has two very good WR weapons in CeeDee Lamb and George Pickens.
PS: What Jerry Jones should do is go sign UDFA WR Isaiah Bond right now. That guy is a separation freak on the field. Him and Turpin would tear things up underneath. No defense would be able to stop our passing threat of CeeDee, Pickens, Turpin and Bond.