I admit I've not used Tangrowth as a defensive Pokemon, but I don't like the grass type on it's own. His special defence is also pretty poor so he isn't a great counter to special attacking water types (which almost always have Ice Beam).Has anybody tried Tangrowth? Regeneration on a pokemon that has better physical defense than even Skarmory is amazing. It can switch into Nattorei with impunity, and at full health can even survive a +2 X-Scissor from LO Adamant Dory.
And he's not dead weight against stall because he can Sleep Powder to help your counters plow through while also being hard to wear down with Regeneration switches. The only problem I see with him is that you can't run him alongside Nattorei, who is probably more useful in this current meta than Tangrowth is.
With Knock Off and Sleep Powder though, he can cripple two Pokemon easily. In Gen 4 I had a nice Tangrowth set that was Sub/Leech Seed/Stun Spore/Sleep Powder. Unless they had a heal beller, it could cripple two or three things fairly easily. It was pretty handy actually.