My opinion would be that it's "doubtful", unless there is an obstruction in your waste line.
Assuming that this is a gravity toilet, the siphon that accomplishes (and completes) your flush is a function of the trapway design, which is molded into the china of your toilet. As long as the waste has somewhere to go once it is pulled through the trapway and falls into the closet bend, and I presume you have the standard slope per foot on your waste line, that's not going to "slow down" the finish of the flush. Neither is improper venting likely to affect what you see happening in the bowl itself.
When toilets swirl and swirl and go down slowly, that's often an indication that you're not getting a good siphon. On old AS toilets, this can happen if the siphon jet hole is blocked, for example. Also, if there's an obstruction in the trapway, this can prevent a complete flush. If this is a new toilet, this could be a function of a defective or poorly-designed trapway, but more likely defective and/or blocked than just "poorly-designed", unless it's some kind of economy model from the Big Box store.
Hard to say much more without more info about the actual installation...
Hope this helps.
(Lucky for you, you live in an area served by one of the greatest plumbers in the country...)