"Which control system is better for tricky lashups? And by tricky I am talking mixing locos that have speed or control system differences."
I've not got hands on experience with lashups, but I can tell you this based upon watching other people do lashups and reading about other people's experiences. Straightforward MTH lashups to other MTH locos or Lionel lashups to Lionel locos are usually relatively straightforward, as you know. Lashing up MTH and Lionel command locos together can be problematic, but this cannot be fixed by using one system or the other. DCS (MTH's system) only operates Lionel locos by "talking" to the command base, so any inherent limitations of the Lionel lashups (much less MTH and Lionel lashups) remain. So if you have Lionel command locos only, use the Legacy system. Using DCS won't improve the ability to control Lionel locos because the Lionel locos are limited by whatever the Legacy system and their mechanics/electronics's limitations are.
When someone says DCS or the DCS app controls Legacy locos better than the Legacy remote or Lionel app, what they are saying is they like the interface better. It is not physically possible for DCS to do anything but control Lionel locos through the Legacy system. Indeed, you cannot operate Lionel locos by DCS without the Lionel Legacy or Lionel command base. You may find, as some mention, that you prefer the DCS interface, but it doesn't change Legacy loco operation one bit.
