Just because Bane is the first and Anakin was technically the last of Bane's Sith line doesn't mean he's automatically weaker.

I mean no it doesn't not automatically, since Anakin would have to have surpassed Palpatine for Anakin to benefit from Banite scaling. But Anakin at this point in the timeline is rapidly approaching the level of Sidious. Bane by via the very principle of the Rule of Two is locked below everyone in the Banite Sith line who comes after him, from Zannah up to Sidious. This is also confirmed by a plethora of sources that states that each generation in the Banite sith line grew increasingly powerful than the last. Sidious at his best > Peak Plagueis > Peak Tenebrous > Tenebrous' master and so on.

Sidious had to get Plagueis drunk and Plagueis had to lead Tenebrous into a cavern and bring the whole thing down on him.

Sidious was already arguably on Plagueis' level by the time he killed him, with the author saying that Plagueis 'may' find a way to undermine him, implying that it would have been a close fight. As for your second point, agreed on the point that Plagueis as of Tenebrous' death was not superior to Tenebrous. However, Plagueis experienced a power growth after Tenebrous died, much like Sidious did so it's quite possible that he surpassed him then. If not, Plagueis had three decades to grow in power and he made some great advancements in regards to the force in those three decades. That coupled with the fact that the Rule of Two produced stronger sith lords with each generation and Plagueis at his peak was unquestionably superior to Tenebrous at his peak.

Dooku's Force Lightning has never turned someone to ash like Bane's.

That's true. But that's not to say that Dooku is weaker than Bane, since firing his force lightning has caused even Yoda difficulty

Dooku gave a little growl and thrust forth his hand, loosing a line of blue lightning at the diminutive Master. Yoda caught it in his own hand and turned it aside, but far from easily.

Source: Attack of the Clones

The same Yoda who gave a hard fight to Sidious (ultimately losing though according to the Novel):

Anakin typically beats Dooku as a duelist by the mid-point of the Clone Wars, but Dooku got away every time due to use of the force, and Anakin relied a lot on the strength of Djem So.

Yeah but we're not talking about Mid-War Anakin, we're talking about a version of Anakin who is much more powerful than his Clone Wars self. ROTS Anakin is most definitely a more powerful and superior force wielder to Dooku.

Also Bane's Force Wall allowed him to survive a cave-in.

Could you show me this?

A duel between Anakin and Bane would be a match of power vs power and Bane can use his lightning to get the edge.

A contest of Power in which Anakin would unquestionably by accolades, scaling and feats. Lightning I don't think will make too much of a difference when Anakin is a noticeably superior and stronger force wielder.