the MESS software list XML files are not 'goodsets' or DATs, they contain information about cart layouts (what is in each cart) and how roms should be loaded for MESS too etc. This allows us to support *proper* dumps of games (rather than deprotected ones, or ones with fake headers bolted on) and is closer to the MAME mentality.
MAME can use Software List XML files too, that's exactly what happens when you run the NeoGeo in multislot mode.
The software lists are more integrated with the emulator than a good set, for example
mess64 genesis -listsoftware
will list all the software that's been associated with the Genesis (well technically anything you can put in the Genesis cartslot on the motherboard, some of it might be region locked and require a different base system to run)
if you open up the megadriv.xml (the softlist used by that driver) you can see things like
<!--
Note from Elbarto:
On the Quackshot PCB there is a 512Kb rom.
Normally all the address lines from A1 to A19 (the whole 512Kb range) tied to the chip in the right order.
But here we have the megadrive A18 line tied to the A20 pin of the rom.
This means that the Megadrive sees the first 256Kb of the rom followed by 0xc0000 lenght range of mirrored/zero-ed data
then again the last 256Kb of the game.
I think they did that for a crappy (really crappy) copy protection.
-->
<software name="quacksht">
<description>QuackShot Starring Donald Duck ~ QuackShot - Guruzia Ou no Hihou (World)</description>
<year>1991</year>
<publisher>Sega</publisher>
<info name="serial" value="G-4054 (JPN)"/>
<info name="release" value="19911220 (JPN)"/>
<info name="alt_title" value="アイラブ ドナルドダック グルジア王の秘宝"/>
<part name="cart" interface="megadriv_cart">
<feature name="pcb" value="171-6206A"/>
<feature name="ic1" value="MPR-14371-F, MPR-14371-H"/>
<dataarea name="rom" width="16" endianness="big" size="1310720">
<rom name="mpr-14371-f.ic1" size="262144" crc="5dd28dd7" sha1="ca02845fa49cd46ccb0a4023b91b10695573668e" offset="0x000000"/>
<rom size="262144" offset="0x100000" loadflag="continue"/>
</dataarea>
</part>
</software>
which as you can see, roughly mirrors the ROM loading inside of MAME and shows how we are able to load a REAL dump of the rom in a Quackshot cartridge, not one that has been rearranged in a fake but working way for use in other emulators (as you'd find in a goodset / nointro set etc.)
things have changed quite a lot in recent years, and it's a bad idea to assume MESS is like other console emulators, it's roots are more firmly in MAME philosophy and the XML files can be quite a lot more than you're assuming.