instead of ignite? meaning you use flash instead of ghost? I feel like, with the way his ult works ghost is almost always superior to flash. His kill potential is always extended with everything being damage over time rather than all in one burst so having a SS that caters to your need to have extended fights (10 whole seconds worth of speed buff). One main reason is that ghost has a much lower CD.
Oh your oppoenent is chasing you? let me give you hope while still being in range for my ult to heal off you b4 having enough MS to turn around and get you if needed
Your opponent is running away after a fight? Unless you also have ghost, I will almost always be able to catch up to you with ghost. Still not enough? exhausting your ass, then throwing out the lazerbird allowing an easy snare if they dont flash and after that you still have ghost (lasts for 10 seconds!) to catch up.
Getting ganked and you are closer to their turret than yours? You can ghost through the sides and they won't catch up generally without hard cc or burning a few flashes themselves or if it's a clown fiesta of 4 people ganking you.
Flash for Ghost? Great now you get your ss quicker for the next fight.
TLDR
Try removing the need for flash, replacing it with ghost, and your options become much greater. Going top lane? take tp. Going against a team that can easily catch you out? flash 2nd choice. got a high sustainer as an opponent (vlad etc)? ignite. Facing an in your face champ (yas, zed etc)? go exhaust facing a champ that can out range/burst you? barrier.
Because in the end you need to be at a certain distance to be effective as swain and flash doesn't really cater to his need of an extended fight and avoiding unnesescary damage while ulting (with ghost it is much easier to avoid skill shots).
Sorry if my talk was a bit too much. Am passionate about swain and helping others become better at the champ I love is also great. Tell me how your games go if you decide to follow my advice of replacing glash with ghost