I currently use Windows Server 2016 on a ThinkPad to handle local mass file storage, DHCP scopes (w/ numerous reservations) and local DNS zones (w/dynamic update support). The laptop used to serve as a Domain Controller, too, but I recently tore that aspect down in favor of modern identity services.
I'm curious, if I take NAS/mass storage out of the picture, what do folks use for local/portable (i.e., not attached to the ISP's cable modem) DHCP and DNS services that support the base use cases I outlined above? Windows is working fine... it's just overkill to say the least. Is there an appliance out there that works well enough?
Arguably, base implementations of these services on Hubitat would be a useful addition... especially given that they're not compute intensive nor storage hogs.
If all we are talking about is DHCP ans DNS that really doesn't need much at all for a home environment. I wouls say some context may be needed to really answer your question fully
That said the Hubitat is the wrong tool for the job even if it is a light weight task.
My middle of the line ASUS home router does DHCP with reservations and DNS. Not sure what local DNS zones are? I think most home routers can do the same these days.
I also run a local AdGuard Home as my primary dns with ad blocking. Similar to a pi hole and I could do without it but like the ad blocking.
You could look at Zentyal Community Edition. It's a Linux based gateway with all sorts of user based file storage, compatible with Windows via LDAP, has DHCP, DNS, etc, and all sorts of other things built in. It's module based and very easy to use.
Then there is pfSense or OPNsense, both based off freeBSD and are both designed for gateway/router duty with DHCP, DNS, etc. I prefer pfSense to the other options, but it is probably the most difficult to get up and running.
You mention cable modem above, so I assume you are also using a router. if so, it should be able to handle your DHCP and DNS needs. I, for example, run a UniFi Dream Machine Pro.
If you feel that your router is not robust enough to handle these 2 service (I don't see why it wouldn't be), then one of the various suggestions above should suffice.
My watchguard handles DHCP and DNS (internet not needed). I do have several windows servers running (for work) but I let the watchguard handle that aspect of it...
I have an Orbi WiFi mesh. The router supports DHCP but bare bones.
A DNS zone is the storage unit for DNS domains. I have two private zones that I maintain at home for work and automation purposes that both leverage dynamic update. My Orbi supports only custom DHCP leased DNS servers, DNS forwarding, and dynamic update to publish its leased Internet-facing address to a variety of public DynDNS services... and that's sadly the extent of it.
Mine isn't that complex but has a few hard requirements. I have ~25 reservations and maintain two dynamically updatable DNS zones with 60+ A, AAAA, and CNAME records used by my remote office and automation setup.
RE: Hubitat being the wrong tool--I hear ya and could certainly make your case as well. But, I'll agree to differ on that one. IP and name resolution are a necessity--no reason for the Hubitat not to offer it IMO. In this way, an entire automation setup is self-contained in one neat little package. Replace your router--who cares. Change your ISP--makes no difference. Matter may further support my case but since it uses ULA addys, I doubt it.
See my other replies--the Orbi's DHCP offering is bare bones and, while it does support reservations, it doesn't offer any scope options (I use 119 for work purposes).
So though that may not seem complex, it is far from typical. Most routers, ect will basically function as a DNS Cache/Relay and may allow some basic setup of hosts associated with specific host names. A fewer number will allow assign a host name to the ip/device itself. That said talking about a, aaaa, or cname records I suspect that will be beyond anything that isn't a true DNS server. I am sure you are already aware of that.
DHCP isn't hard and can be handled easily, it will be the DNS concerns that will cause problem.
I'll leave you to work w/the pros on this, beyond my pay-grade. 
