Well, there are still issues with certain champions, mainly assassins and some adcs, who build both items to shred through a tanky team. While I'm not against them doing some kind of relevant damage to tanks, they shouldn't be able to ignore so much armour.
Aditionally, the mechanism used for procing the shields on both maw and steraks are different, but only one will apply because they are bought to fulfill very similar roles. Similarly, the hydras both only allow the use of one of their passives or actives at the same time because they are intended to fulfill very similar roles. The same restriction, or at least a similar one should apply to different kinds of % reduction / % pen of armour that every champion can purchase, to prevent excessive synergy with two items that are meant to fulfill very similar roles.
And i know they recently changed cleaver and LDR to have worse stacking stats with eachother, but there are still cases where the two items when built together can be overbearing.