(After January when the sync bug will be resolved,)

The only thing that can make a node's RAM consumption skyrocket (as in
increase 5x above average or beyond) would be transactions, right?

To that end, if I wanted a node with stability guarantees, could I just
make it not listen to transactions (not relaying them is fine!) but
instead just record blocks?

(Or, store transactions to persistence, intentionally knowing that that
will sink performance but guarantee stability?)

That way, you get like a "blockchain database server".

Thanks