Trying to compare classic client vs retail client capabilities

[Salt 1]

I'm wondering about modding capabilities of the classic client. The _lgt(wdt) files for instance. . They are present in every map directory, but seem to be empty and they have no version. I've tried all 3 formats MPLT, MPL2 and MPL3 but none of them seem to work. Does it perhaps have it's own format? Or maybe it's not even being read by the client similar to the _fog files as noted on the wiki. How do you even figure that stuff out? I'm not sure how to debug without crashing or even in general lol. 

I assumed classic would retain many of the modern functionalities as even the DB2 structures are very similar or even identical and it just seems good for consistency.  I couldn't just model swap with anything above > 2.4.3 either from retail to classic and it appears because there is just extra unreadable data in the M2. Things like physics,  particles, shaders and whatnot might not be functional  either.

I have to say I'm not very familiar at modding modern clients.. am I just missing something?  A bit disappointed if this is the case because I like the base of the classic clients a lot more than retail.