Are they contributing a significant part of their DPS though? If they are that goes against your notion that Blizzard has some issue with passive damage. I highly doubt that 6-8 imps lobbing fireballs at my primary target aren't passively contributing a significant amount of DPS for me.
I don't remember what I said in regards to the amount of the overall DPS it should contribute, but it should be significant, like Imps within the demonology spec. As for the situations you mentioned, that seems like a case of cool down manage like any other class.
I do think the Tinker should have an ability that allows them to drop a pre-arranged array of turrets at once, like what the Shaman class had with their totems back in the day.
They're turrets, not totems. As for the upgrade, that should just be a CD you press. What? You thought it was going to be like that character from Overwatch who sits behind their turret and hammers it into an upgrade? No, it should be a CD that you can press and it will automatically upgrade your totems for a relatively short duration.
What??