We'll come back to that piece of logic in a bit, but let's start with the purpose of things. I assume you mean by this that there are objects that perform certain functions particularly well.
This is true. However, that tends to only be the case when you're comparing them to naturally unevolved items. If you think about them as items that have been designed, then you'll find that actually you can find all sorts of what would be considered design flaws.
Even given that we're not necessarily talking about a Christian omnipotent/omniscient god, a being that creates a universe should probably be designing on such a high level that our squishy little human brains shouldn't be able to find much wrong with it.
Take for example the human eye, which often gets used in these sorts of things. Seems pretty amazing, a little ball of jelly that lets us see light. But if you look closer then you find that actually the "wiring" runs in front of the "sensors" in the eye. It's mostly transparent, but it obscures some light and makes our vision worse. There's no need for this, the octopus does it the "proper" way.
Name something that you think is a good example of purposeful design, and I practically guarantee that someone can think of a way that it could be improved.
Here we are back to your first piece of logic.
If you're going to say that causality must be maintained at all times, then you don't get to throw that away because it makes it hard to explain god. If you're willing to accept that god might be eternal and has always been, then you have to be willing to accept that this might be true of other things. Including the universe. To do otherwise is to cherrypick where you want the rules to apply, and that's no good way to find the truth of anything.