Shoretrooper is fairly dated nowadays. One of those units who's never bad, but not really worth it anymore. Ends up displaced from both troopers and Palpateams. And in most cases Stormtrooper is the better tank despite the pretaunt.
Pretaunt isn't especially valuable to Empire as a faction because you have two main Empire teams. Palpateams almost always have Vader go first due to his unique, then Force Crush/Culling blade to feed TM to the rest of the team. Pretaunt doesn't help much. Troopers rely on modding Starck to be faster than the enemy party, then using Starck and Range to buff and give TM to the other troopers to land a kill early and steamroll. Shore doesn't contribute to that win condition. Stormtrooper isn't ideal for either team, but will have time to put up taunt in either case and drains TM when hit to help you keep momentum.
For a Palpateam? Your lineup is fine for the point in the game you're at. A tank wouldn't improve your situation much. Your next step is to get out of Palpatine and run a different arena team. Bastila is a good next step, or JKR if you can get them before your Bastila team is arena ready.
Longer-term for a Palpateam, you're looking at Palpatine, Vader, Tarkin, TIE Fighter Pilot, and Imperial Probe Droid. Specifically, this lineup is good for taking out Padme teams. Vader lets you outspeed and land/clear a bunch of debuffs, kickstarting your team. zIPD and TFP both give you sources of buff block, with IPD clearing buffs at the same time. No out of turn attacks that would trigger locked protection up. All in all, it's the highest-value team you're reasonably going to get a Palpatine team to take down. The main tweak you can make is replacing TFP and Tarkin with Deathtrooper and Krennic, but Krennic really isn't worth it these days and you'd be pulling Deathtrooper from Troopers.
The other Empire team you can field in parallel is troopers. Right now the ideal lineup there is usually Veers, Starck, Rangetrooper, Snowtrooper, Deathtrooper. If you're running Deathtrooper with Palp, sub in high gear Magmatrooper (he takes high gear to get his damage up and really come online) or Stormtrooper. You need Starck faster than the enemy, Rangetrooper at least 80% as fast as Starck, and the rest at least 60% as fast as Starck, modded for high damage output. Starck buffs, Range buffs, then you have three turns to land a kill and initiate trooper roll. As long as Starck goes first and you have enough damage, there isn't a whole lot bar major meta teams or beefy pretaunts that this lineup can't kill.
The third Empire team you can field and get use from is niche. You need a high-gear Magmatrooper modded for potency, tenacity, and damage. Run under a fast Thrawn lead. The rest is more or less arbitrary. This is specifically to counter zSion, usually seen under Traya. Every turn Magmatrooper damages Sion, he gains 70% TM from his unique and another 20% from Thrawn lead, and he has an AoE that can drain TM from the entire enemy team. Loop to death and glory.