A lot of people tend to overestimate how good they matchup against Mardu vehicles. Sometimes your cards will line up well against them, but other times they will have a multi-avenue attack. Scrounger, Vehicles, Gideon, and potential counterspells all present different difficulties. In addition, their natural aggression makes it tough to perform your combo. I'm not very experienced with Jeskai Saheeli, but it might take a meta shift for it to come out again. BG and Mardu seem to be dominating right now, with some Marvel decks (4 color?) being the wildcard.