Rom 11:36 has διά + the genitive which can be translated "through" or "by." Either translation is able to communicate the notion of intermediate agency.
Col 1:16 is also διά + genitive and Heb 2:10 has this construction too (δι’ οὗ). Compare Heb 1:2.
What will determine how one renders the construction should be context or translator preference. But, as I see it, nothing is wrong with communicating agency with "through" or "by." BDAG shows that διά may be used as a "marker of instrumentality or circumstance whereby someth. is accomplished or effected, by, via, through" (224); διά can also be a "marker of pers. agency, through, by" (225).
In John 1:3, 10; 1 Cor 8:6; Col 1:16, διά is applied to "Christ as intermediary in the creation of the world" (225).