Tsubasa and radiocool have a fantastic moveset for Swellow but moves like roost, agility, and tailwind just simply aren't moves that I would recommend (no offense of course). Swellow just isn't bulky and is way too frail for those kinds of moves. Just give him an all out sweeping moveset and you should be fine
EVs: 252atk, 252speed, 4hp
Item: flame orb (goes well with guts)
Brave bird: 120 power but does recoil (definitely worth it though)
Facade: Does 140 damage if you have a status infliction (Flame orb's got ya covered :p. Goes good with guts as well)
U-turn: Im out of here folks!
Steel wing/pursuit/protect: Coverage, attack when foe switches out, or stall for one turn to get flame orb started? Choice is yours.
So yeah very similar to tsubasa and Radiocool's moveset.