Great ideas and propositions, but I feel both classes would benefits from playtesting and a bit of fine tuning.
The Champion ability to use all weapons is a bit strong. Maybe the could be able to use all melee weapons and crossbow as a range options?
As for the Martial Artist, I feel they should have a way to improve their AC. Right now, with a lucky Stat roll, their max AC is 14. Since they can't wear armor and they only a 1d6 HP, it doesn't bode well for them in fights.
Overall, great ideas, but a bit rough on the edges. Good work and I hope you continue creating!