You might not replace the cat actually. At least not for a very long time. The difference between summoned augments is very very small. Switching from something like the cat to a bulette pup is going to be very low on your end game priority list. However, getting a deepcrow hatchling for the offense power is also going to be on that list, for a dps anyway, so starting with one kills two birds with one stone.

If a brand new player is on a tight budget there's nothing wrong with starting with a cat, or some other cheap augment, and keeping it for quite awhile. Most likely through mod 19-20 depending on play time and how quickly everything else gets upgraded.

The purpose of an augment is to give the player 40k or more in every stat. All of them do that at legendary with high rank bondings. Which stats they add a small bonus to on top of that is fairly inconsequential.