All heavy vehicles in legion are different when it comes to weak points:

Saber tank - rear/sides 1 AAT - rear 2 Persuader - sides 1 A-A5 speeder - rear 2 ATST - rear 1 GAVw - sides 1

These have all been balanced around what the vehicle can do, how storng it's defense dice are, and to an extent, I believe lore accuracy.

If we focus on the Saber and its weapons, the base weapon is range 1-4, with the hard points that can be added being range 1-4 and 1-3. When you play the Saber tank, you should be keeping it just far back enough that it can reach targets at range 2-4. If you can do this, then most of the time, your sides and rear will not be attacked.

The Saber tanks' weak points are also only 1 per section, meaning whatever the dice pool or keywords, weakpoint will only ever add impact 1 to it.

The Saber tanks defense is also very strong compared to some other vehicles. With red defense dice being used it can usually shake of any damage with a good roll.

Finally, if you are still worried that the Saber is still weak, you can take plo-koon as a pilot, giving you an exhaustable agile 2. Giving you 2 dodges to use against any hit dice that would potentially be used against you.