Ion suits the peekaboo style well. I have very little success engaging at close range, even 1v1. You want a good distance, and you always want some cover, especially against Tone and Legion. Use the laser at close and long range; think of it more like Ion's version of the Tone rockets, which is helped by using the perk that charges your energy if you get critical hits.
You don't really want to ADS the splitter too much, as the energy is best reserved for using the laser or tripwires. Speaking of tripwires, they are great for annoying and denying Ronins and Scorches who can otherwise wreck house in chokepoints.
Vortex shield should be used reactively, not predictively, because if you try to predict too much, you'll waste a ton of energy and therefore your main DPS: the laser. Try to get a feel for when Tone's rockets will come, or at what times they'll probably have a Salvo core. Your laser core is your "oh shit" button, for when you get cornered unexpectedly. It works great on pilots flying through the air, as well, if you manage to make one eject.