I did the numbers in a Google Sheet and come to the conclusion that a lethality smolder build in 14.23 is definitely viable.

https://docs.google.com/spreadsheets/d/1HGCMgy479taaGKH-u7xQMj7ZG0pbJ4E2-5fBkRib1ts/edit?gid=0#gid=0

The numbers and the Items are all in the spreadsheet, but to quickly sum it up:

I did make a quick Lethality smolder build that primarily focuses on AD, Ability haste and Lethality. The items are Essence reaver, Hubris, Seryldas Grudge, Voltaic Cyclosword and Oppoturnity. I personally found that those items synergise the best with his kit.

The results i got were that while Crit smolder does more raw damage on his Q and has higher range due to rapidfire cannon, Lethality smolder does usually more damage with his other abilities and the 2 percent more Q burn due to way higher AD while having more ability haste. On top of that, the almighty 51(!) Lethality combined with the 30 percent armor pen effectively reduce the armor of any squishy by 80 percent. And this build has some build in slows which make it far harder to escape for enemies.. The build is potentially the best in very bloody soloq matches due to hubris. Oppoturnity also makes his E excellent as a finisher due to the movementspeed buff stacking with his E. To be clear, you dont need to build all the recommended items here, a hybrid build is likely also completely viable. This is just to demonstrate that Lethality items are absolutely an option for smolder. (For the sake of transparency I should mention that the buff from spear of Shojin wasnt calculated in the crit build, but if you want i maybe can add it. its just i am a bit new to excel and didnt want to overcomplicate it.)