Those are some of the things I anticipated. My previous car had a fully powered 12" in ported enclosure so I knew that 8" wouldn't compare.A couple things are happening here. The first is and it applies to all car audio is shallow subs will not produce the punch that a full size sub will. They just don't move a bunch of air. I am running a real nice 12 inch shallow sub and even here you don't get punch. Even with 500 watts driving it it won't rattle the vehicle. If you want punch you need a full size sub.
But the biggest problem with the factory Alpine system is the head unit/amp rolls of the lows very early, probably around 125 hz. This is done to keep the factory system from rattling which the factory sub enclosure will do if you get a good signal to it.
Many way to address this with installing a new head unit probably being the easiest route. I just ripped the whole system out and started over.
It seems that most everyone on here feels that replacing the alpine sub created a better sound quality and that's what I was hoping for but thus far it seems that the alpine sub was better.
I think I just need to give it a week or so to be sure. I have a 60 day return on the sub I bought so I've got time