Three persons involved in one event
How is this supposed to be evidence of ontological unity? Two men and God can be involved in growing the church (1 Corinthians 3:6-8), but that doesn't imply they have ontological unity. The argument from these verses appears to be that the three persons are one actor/agent. However, it's not clear how this is distinct from saying they are one person, which is modalism. Moreover, it is easily disproved that they are one actor by the fact that they have different roles in creation, the incarnation, etc. They can only have distinct roles if they are three distinct beings.
Lexham Survey of Theology
Additionally, Scripture speaks of all three persons of the Trinity as being involved in the creation (Gen 1:1–3; Eph 3:9; John 1:3; Job 33:4), the incarnation (Luke 1:35; John 1:14), the resurrection of Christ (Gal 1:1; John 10:17–8; Rom 8:11), and the sanctification of believers (1 Thess 5:23; Heb 13:12; 1 Pet 1:2).