many statistical functions and elements extraction are

very different for data in the both forms

Several examples

sum()

denote

list lis = ...

sum(lis) is essentially the same as sumr({lis})

but sum({lis}) is different

In the opposite direction:

analogue of sumc({lis}) is aggregate(lis,const,"sum")[3:]

mean()

In the contrast to sum() it is not allowed for a matrix

Again, mean(lis) corresponds to meanc({lis})

Overall mean for a matrix of general shape is meanc(vec(a_matrix))

The behavior of min and max is similar to that of mean

Overall median for a matrix is quantile(vec(a_matrix),0.5)

In my opinion, it would be much transparent

if sum() mean(), etc were overall sums and means

   and sumc(), sumr() etc were defined both for lists and matrices

   these functions could have additional boolean/integer parameter

   indicating how to treat missing values