>>10352562-rail O is DCC everywhere.
Lionel has three systems--and the first two (Trainmaster CC and Legacy could be considered to be one since the latter is merely an expansion of it's predecessor, with additional command codes not accessible under the older system).
Lionel's newest 'system' (LionChief/LionChief+)is essentially 2GHz radio control for mid-range starter sets and separate-sale mid-range locomotives. The "+" denotes an ability to run conventionally without the dedicated remote (limited to separate-sale locos). While LC/LC+ will run independently on any command layout, there are no plans to make it controllable with anything other than LionChief remotes.
MTH's DCS is it's own system. Second-generation units (Protosound 3) include DCC receivers integrated into the electronics and can run on either system out-of-the-box just by flipping a switch. Every MTH loco, from starter set units to finescale is equipped with this system.
(some MTH diesel locomotives are also available as 2-rail or 3-rail with trucks equipped to accommodate separate-sale 2-rail finescale wheelsets. MTH European units are similarly convertible, but is mostly 2-rail with a small number made in 3-rail for the US market.)
"incompatible" implies (to the uninitiated) that the two systems cannot co-exist. DCS and Legacy/TMCC can operate in tandem on the same layout (photo), and DCS can operate a Lionel control box to control their equipment with the functions common to TMCC and Legacy.
Both platforms now have WiFi/smart-device control options that will eventually allow operating both systems' functions from either platform. (except LionChief/LionChief+)
