Indeed, A2000 was developed from German based team which took A1000 as starting point; they deleted monochrome video output (rev4.0 was last one to roll-out from that team).
US based team got involved a bit later to start B52 as a direct involvement of Rattigan's visionary acts supporting cost reduction of Amiga in general, so US -based team took over A2000 from Germans and redesigned it by using A500 components which became available in meanwhile.
As mentioned before, they spared every damn cent wherever they can find one and that literally means they omitted a single RCA socket (monochrome signal was always there at a pin#19 of video encoder chip). A520 became a part of usual kit (unit, mouse, power supply) in Q2 1989 at the end of Rev5 assembly lifecycle, when they introduced 2 special editions.
A520 used then one of available, off-the-shelf Motorola encoders (MC1377p) which were known to be mediocre compared with true RGB signal quality. Even by modern standards, you can use either Philips SAA chip or Analog Device AD724/AD725 for much better image quality (as DIY design), but you're still lagging behind RGB. S-VIDEO was possible back at times just as A520 were introduced as a hack which involved heavy unit modification.
