Note: This guide is mainly more for me to just have around than anything else, feel free to use it.
I've gotten above 700k and even gotten 900k in gold tier with only my two pdb rhinos. When you're using a pdb, you have to know when to flank, run away, and when to put your shield up or down.
Run away if a db rhino is 320 m in front of you. Flank when you see another rhino(even db and db variations, you'll take him out before he can do enough damage, especially if he's distracted by your teammates) or more than three enemies. Put your shield up when reloading your taran, during a stalker's stealth, against a thunder until it slows down, when travelling between kills, and against a pdb griffin until the tarans run out, but keep your shield down all other times. Your shield should also be used when there are snipers on the enemy team but no enemies around or when travelling towards snipers. No need to take unnecessary damage.
The shield on a pdb rhino should be used offensively, not defensively. The only boost you should get from the shield is speed, braving sniper fire, and defense until a pdb griffin runs out of taran juice or until a boa thunder taran runs out of thunder and taran juice. The biggest mistake I see when facing other pdb rhino pilots is that they rely too much on their shields. You have failed if you are just tanking damage from an enemy pdb rhino with your shield. You should always try to flank another rhino when in a pdb, even if you have to let your teammates take a bit of damage.
However, there is a way to deal with pdb rhinos even if you have not flanked him(turn back and run if it has orkans, tulus are okay). Rush slightly to the right or left of him until you get past his shield, once you do that, then start circling around him. Most of the time he will try to turn towards you in a futile attempt to block the damage, but even if he drops his shield, you will still win since you got the first shot off. If he doesn't start moving but still has his shield dropped, then it will still be possible to circle him. If he does start moving, then try to zig zag in place, this can cause him to miss a couple of shots.
When running away from dbs, you have to run before they get within 290m, otherwise, you won't escape. Once you've run away, get behind cover as soon as possible.
And if possible, try avoid combat at ranges of 100m and below if your opponent isn't a pdb rhino. At that range, aiming gets harder(especially if your enemy is a medium or light bot circling around you) and a thunder will out dps your plasma loadout.
When facing a rocket enemy, wait until he is distracted and focused on your teammate. By then he will probably not target you and you can safely take him out.
Another thing to do in apdb rhino is to try to predict what setups your enemy is using. If the enemy is hiding behind a corner, he is either a db/rocket setup or a thunder carnage/lancelot. If he is a rhino but is using pinata with his shield up, he is probably a db setup and you should run immediately. If he is using magnums but you can't see taran tops peeking out from the top of hie shield, he is probably packing orkans.
The best way to deal with a db/orkan griffin is to ambush it. But if you can't run backwards when he starts firing at you then run forwards if he jumps towards you or to the side. You may be able to get below him and avoid a bit of damage, giving you time to take him out. If he jumps backwards, then initially run backwards until you get out of 300m from him. Then, get within 340m and try to take him out from there. Remember, the db griffin is screwed if its orkans run dry and its jump is exhausted as it has no shield to defend against your plasma.
The pdb rhino is a flanking and defensive bot, not an all out assault and ambush bot like the db rhino.
I love my db rhino, but there's a reason why I have two pdb rhinos.