If the adversary can see both your connection into the network and the results of your connection then it's likely that they will, given time, be able to deanonymize you with some level of certainty. This is a fundamental limitation of all (known, at least) low latency anonymity networks.
Picking a known-good entry point will defend you in cases where the adversary doesn't have good network visibility of large enough portions of the network. In that case they could try running a set of entry nodes and some other point of interest (exit, hsdir, etc). By doing this, you'd remove their ability to link the traffic back to you. They might be able to control the "exit" and the middle node but since they don't have network visibility they'd have no means of linking it back to you directly, at best back to your known-good entry point...but there's the rub.
In your stated example of either running a private bridge yourself or having someone you known to run the private bridge, given that an adversary was able to track it back to the entry point, the entry point itself would have a restrictively small set of users. Thus, the fact that you are using the private bridge would reveal information about who you are, at least reducing it to a small set of possibilities.
To this end, if you have a known-good guard then you'd have a better anonymity set in the case where they were able to successfully discover your chosen entry point. However picking your own guard comes with a whole other set of potential pitfalls.
However, in all cases the first point still applied: if they can see enough of the network then you will still lose.