Which possible buff does not break the gameplay of Turks?

There are lots of people wish buffs for Turks, Khmers, Vietnamese, or etc.. Some of them seems feasible but pro or decent gamers says that it breaks gameplay or make them OP. Some of them seem good but actually useless. I have not played as Vietnamese or Khmers very much, that's why i don't know what they lack. For Turks;

1- Onager upgrade,

2- Artillery affecting Mangos (7+2 range),

3- Sipahi affecting Hussars (may include LC or not) (+20 HP).

Turks are worst in trash wars. I thought "one" of these techs may make them better a little, not a huge difference. What are your opinions?