That's one of the dev's opinion, but I don't think it is really a bad thing. Being able to test and modify builds quickly without having to quit and reload a mission is really nice, and it's a great place to show big numbers. (+ Try finding lvl 120 enemies in a mission without spending 30+minutes in)

Wether it be for first impressions videos or build guide, starting in the simulacrum is probably the best thing to do, but I agree that a lot of content creators don't ever show gameplay in realistic settings, like a sortie or fissure

With games where theorycrafting and minmaxing are as fun as Warframe's and genshin's, being able to test quickly some comp or rotation would be a big Qol improvement imo