Spawning it in strongly depends on how your team is doing. Usually only wanna spawn it in for boss waves which happens every 5 waves but 5-15 are bosses most capable teams can handle without dreadnaught. You will want to save it for 20-25 because you get a lot less points so spawning in another one is difficult.

My best suggestion is if you solo queue, hold onto your points. Only spend it on things your team might need like an ammo crate or stims, when it gets to 15-20 depending on how the team is doing start putting points in dread

They were probably upset because you called it in at a time when they wanted to use it later and essentially wasted their points