If weqatal is nothing but qatal which happens to have a conjunction,
why are the instructions for building the tabernacle (for example)
full of weqatal's and yiqtol's but no qatal's; where the corresponding
account of the building is largely identical except that it has
wayyiqtol's and qatal's but no yiqtol's?
If we look at the clause level, I am not sure how to account for this
data apart from a "traditional" four component model with something
like a "waw conversive". Then there is a separate issue of deciding
how this strange system arose (but there are many very strange things
in real human languages!)
If we are to move anywhere beyond such a traditional view, I am sure
we need to look above the clause level. So my advice to Dave would be
to brush up his discourse studies before taking his studies further.