Shadows don't get a huge endurance boost, only 3% from the tree and 25 from Shadows Training, most Shadow tank gear was previously itemized to be high endurance and ideal Shadow tank stats (as per KBN's work) involved ~28k HP. Add in the HP boost from gaining 5 levels and 30k sounds about right for a Shadow. Quite high for the other 2 tanks though. My Guardian didn't crack 30k stimmed until I had 2 or 3 69 pieces but I was also mostly mitigation stacked with only had 24.5k HP unstimmed at 50.
My juggernaut in full 66 (though crafted mods/armorings/enhancements) with Black Market MK-2 implant and the Rakata stim is at 30,5 k health. And no, I did not sacrifice mitigation, as I'm only 60 defense from ideal tanking spreadsheet.