The default runtime environment configuration for the cardano-node on which Daedalus performance most depends is, as far as I can tell, limited with the -N option to 2 cores (or 1 if you’re on ARM architecture):
It’s hard to tell whether these default build parameters are in the currently released Daedalus, but I can say empirically that Daedalus will only ever use 2 cores on my 6-core machine… though it distributes nicely between those cores so it only uses ⅓ of each of them. 
I’ve asked in this forum before how we might be able to tune the network or performance settings of Daedalus, and got no response either from Daedalus developers or third parties more knowledgeable about Daedalus internals…
… though not being able to modify these configuration files could well be part of Daedalus’s well-audited security architecture. If I had my way I’d have a Daedalus UI option to start cardano-node with the -N option instead of a hard coded figure like -N2 so it would use all available cores. 