Not only Mona+Anemo can run further than Mona+Rosaria+Diona, the whole run is also a bit faster (0.6s to be exact). And yes, I do have Diona's talent at 7lvl.
If you want to use Mona+Anemo and you are wondering who should take the last spot then the difference between Rosaria and Diona is marginal, Rosaria is much easier to use since it's a passive talent.
The necessity of having to switch to Diona almost outweighs her less stamina consumption bonus, but if you can switch back to Mona as soon as the shield gets created she will be the optimal choice.
I have assumed that Diona's skill description is incorrect and simply using the charged-up skill gives you shield with it's maximum duration. That's not the case. The skill states that it needs to "hit it's target" which is true, but even the ground or a wall is considered a proper target. Just don't let the projectiles disappear in the air. ¯\_(ツ)\_/¯
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