Thanks for bringing these up, there are really good points. It pays to actually be working on a use case, instead of just collecting data and enjoy how pretty they look. 
There are two issues you are mentioning:
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Inconsisten denominator units in DRUG_STRENGTH. We do currently have 16 such cases, where the different ingredients of a fixed combination drug product have non-matching units, for example 42799258 “Benzyl Alcohol 0.1 ML/ML / Pramoxine hydrochloride 0.01 MG/MG Topical Gel”. I can imagine how this happened: The original product information probably gave the content in %, and RxNorm then applied its conventions by which % of a liquid (benzyl alcohol) gets converted to ml/ml, and the % of the solid ingredient (pramoxine) gets converted to mg/mg. To be honest, I am a little bit at a loss how to fix that. In those cases, we could just replace the ml/ml to mg/mg and be done with it (can’t do the other way around because ml/ml doesn’t make sense for a solid substance, unless you melt it). Let me know what you think.
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Unit of the quantity field in DRUG_EXPOSURE. This is actually currently not properly defined in the OMOP CDM. In the US claims data, where this field originated from, the convention seems to be that for solid products (tablets etc.) the quantity refers to the unit of drug (tablet in this case, or “pieces” as you call it), while the liquid products seem to be referring to the denominator unit (mL in most cases). At least, that seems to be the case in the claims data I have access to: PharMetrics Plus. @dtorok, @ericaVoss, @Patrick_Ryan, could you be so kind and look at the various MarketScans and Optums and check it out?
Let us know what you think. I will enter this into the list of CDM improvements. Please fill out the detailed page, so we can toss it around in the community and get it done.