#4 RAW can gain its 'flagship' show reputation back
If AJ moves to RAW, lets assume after WrestleMania 35, he won't need many feuds to progress towards the Intercontinental/Universal title picture. RAW desperately needs a champion who can perform as the face on a continuous note.
AJ's inclusion allows the low-carders to put up a great match and extend their viewership. For instance, feuding with Bobby Roode/pairing up with him as a tag team allows Bobby to gain high-quality booking.
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Since WWE is planning a mega push for Drew McIntyre in 2019, what better way than to have a feud between 'face' Styles and 'heel' McIntyre? They both have the calibre to put on an instant classic inside the ring, and can cut good promos before the match as well.
The storylines of RAW mostly revolve around Seth Rollins, Dean Ambrose, Braun Strowman, and Brock Lesnar as the main event. Adding AJ Styles to the card will allow them to shatter headlines and prove RAW to be the 'A' show in the days to come.