So your using RFC 2136, with bind right? I do not believe unbound supports that method of update.. So yeah there are some differences and depending on what your wanting to do unbound is not the best choice.
If what your wanting to do isn't supported by unbound - then yeah I would concur setting up bind is good choice.. unbound not really meant as authoritative ns anyway. If what your wanting is authoritative name services on your local lan - bind is going to be the best choice again..
Also the dhcpd gui config in pfsense does not expose every possible config scenario either. So yeah when you want to do more fancy stuff with dhcpd - run it on another box is always great idea.
I think there is a bit of misconception in some of these services that pfsense provides that are really outside the scope of a firewall/router... While sure its nice to provide features like dhcp and name services - makes it really easy for small shops and less experienced admins... But in the big picture as the size of the network grows - such services are almost always hosted elsewhere in the network..
I do not believe the end goal of pfsense is to be the end all get all do it all box for all network services a network might need.. with every possible configuration of dhcpd or dns to be exposed via a simple gui.
And since the configurations are started in the xml, and specific things to provide good setups while its possible to adjust the scripts that setup the configs, etc. to do uncommon things - if what your wanting to do is outside the scope of the gui interface to these services provided by pfsense.. Yup run them full on some other box in your network..
If not too crazy of a thing - you could always put in a feature request or bounty to get some feature or configuration functionality exposed in the pfsense gui for for that service.
In unbound you can do good stuff in the custom options box - but depending on what your doing that could become cumbersome.