21 is one of the best anchors in the game currently and Trunks has always been a really dependable mid or anchor.
17 A/ Trunks A or B/21 Any Assist sounds like it could be pretty nasty. 21 A is a high blockstun, single hit assist now, so it can set up some unique pressure for 17 and Trunks while also working as a combo extension/ neutral assist.
Might be hard to stop people from holding upback against you if you don’t pick Trunks A but, overall sounds pretty solid to me