At thing point, since the dados are already cut they're the most practical solution. I suppose you could also do a blind tapered sliding dovetail with a housing but the dado is already fairly deep you might be making the case sides pretty thin at that area.

Since you are this far along and adverse to visible joinery I might simply forgo any changes to the plan and just make a mental notation that in the future if it does move away you could use dowels and screws to bring it back together.

I like tapered sliding dovetails a lot, they're especially practical in these sort of applications because they do not add to the stress of the glue up. So you glue up your dovetailed case, then after that's set you can start adding those dividers in, which allows you to fine tune them in terms of length and fit.

My first sets of large case goods I had made them so that the caseback was integral and side joinery came together all at once, it was incredibly stressful, so after that, even for small projects I decided to start taking steps to make it much easier though admittedly more complicated in the planning stages.