As long as WeChat is the only messaging app allowed in the PRC, it will be able to get away with far more than any other app. It doesn't make any sense to compare niche productivity tools to it.
It makes complete sense to compare because Apple likes to claim that it imposes its rules and guidelines perfectly uniformly.
I'm not defending this particular frustration of iOS App Store policy. But it's worth recognizing that there is a balancing act going on here. Apple and Google are in the difficult position of trying to balance reasonable security policy with people's freedom to use their phones as they want.
If there is a happy medium between where Word Processors are also virus vectors and the walled gardens we have now, I don't think anyone has found it.