I did not say Toxapex and Venusaur don't check Celesteela, I claimed that Tentacruel punishes Celesteela for clicking Leech Seed while the other two don't. Celesteela will never stay in on Venusaur unless it is running Air Slash (I mean I get that steel has issues with ground, but really, AV?), so Venusaur wouldn't get to click Leech Seed against Celesteela. There is nothing really punishing Celesteela for clicking Leech Seed against a team with just Venusaur, but if it clicks Leech Seed and Tentacruel comes in, whatever Celesteela goes into to try and avoid getting whittled down will continue to lose health from the mistake of clicking Leech Seed against a team with Tentacruel. For variants of Celesteela lacking Earthquake, there is no negative to bringing in Tentacruel. I did explicitly mention in my previous post that avoiding sending the game into a war of attrition (as Toxapex often does for the things it checks) is one of the reasons why someone could opt for Tentacruel over Toxapex.
Also, check out some of Bit's games with offensive poison, the archetype functions fine, AND it doesn't call for 60 turn games. If for some reason you deemed it necessary, giving an Air Balloon to Tentacruel gives it a one-time ground immunity and it's actually capable of punishing the ground moves it switches into unlike Crobat (and for Pokemon other than Diggersby which can easily spam frustration against poison, Landorus-I which Crobat fails to beat many variants of, Choice Banded Excadrill, and SD Garchomp which is in the same boat as Landorus-I, Venusaur already acts as a check. And for all of these Pokemon (other than Diggersby) , slapping an Air Balloon onto Tentacruel on an offensive team is more likely to be effective in stopping the threat than Crobat is).
Also, spamming Adaptability Draco Meteors does absolutely nothing for poison as the types that aren't capable of one shotting Dragalge before it gets off the Draco Meteor are types Poison is already beating or have moderately effective switch ins to the attack. Golbat is an inferior Crobat that is easily taunted and takes the same hits that one of either Venusaur or Crobat do (and without the loss of momentum!). So frankly, Tentacruel is more useful than either of the two for actually accomplishing something other poison types don't (getting rid of opposing hazards without getting rid of your own).
It absolutely can't be fit into balanced poison, as I implied in my previous post and throughout this one, but it has a niche on offensive poison (which as Bit has demonstrated to some degree is a viable archetype).