Both Con & Lab policies are, in fact, simple:
Con: Trust Boris Johnson to deliver Brexit.
Lab: Don't trust him, trust us. We'll do it better. And because there's no mandate for one version of Brexit over all the others, we'll put our deal to the people for a final say. https://twitter.com/JamesDMorris/status/1200095757157773312

The first part of Labour's argument should be straightforward: can you really trust Boris Johnson? The second requires a small amount of nuance on two issues: the need for another referendum and Corbyn's 'honest broker' stance.

On the referendum, Labour needs to explain that the narrow 2016 vote masked a world of difference between different kinds of Brexit, with massively different outcomes for people depending on which was finally chosen. Once the choice is made, a final vote is the right thing to do.

Then Corbyn must explain why Cameron's resignation was both inevitable & wrong: Brexit is a major national decision, deeply dividing the country; government must implement the outcome, whatever it is, & continuous leadership is vital. An 'honest broker' PM makes that possible.

Compared to the deceptive simplicity of 'trust Boris Johnson to get Brexit done', of course Labour's extra steps add complexity, but necessarily so. It puts them on the right side of the argument, even if that argument requires more effort to articulate.