Its main gun has the lowest dps
Absolutely irrelevant, it does the exact same damage as sm/chaos predators.
https://dawnofwar.info/codex.php?page=elite/leman_russ
https://dawnofwar.info/codex.php?page=elite/predator
https://dawnofwar.info/codex.php?page=e ... s_predator
On top of that with the patch it gained +15 sight range (all other tanks have 40 vs leman's 55), so the upgrade it used to have has been integrated in the main cost (upgrade that was a 100% must buy), the leman or multiple of them are still harder to deal with than a BB due to their maneuverability and have better killing potential of both enemy vehicles and squads due to it's speed.
And I haven't yet taken into consideration on maps like Outher Reaches where a baneblade would be absolutely unplayable.
And on top of all of this it retains the "free" low dps lascannon on the front, so the leman is still the best tank in the game, except that now it will take a longer to repair and multiple lemans are still often the better and safer choice than a single baneblade and if anything with the HP and damage nerf the BB got hit by it feels significantly inferior to other superunits or even tanks.