MB52 is not any better, those reports all serve certain needs, but none of these needs is to get matched with Financial postings.
I just recently posted a link to OSS note 407812, which explains the logic of the displayed values.
And the LIS statistics are even updated asynchronous,independent of the material document and financial document. If the update of LIS fails then the transaction is not rolled back and you get an inconsistency and only rebuilding of the whole infostructure could help you little further, but even this rebuilding has some constraints.
MB5B is eventually good to analyse the history of a single material, focus on quantities since it is an inventory report, and this takes already quite long, I can't even imagine to run this monster for an entire plant, this would take several hours. It cannot work with serial numbers, it does not consider stock in transit, it struggles when you archived the zero batch stock segments from table MCHB etc etc. just read through the OSS notes.
The only accurate transaction to compare MM and FI is MB5L, as this is made for that purpose.