Hi Laurens,
I can reproduce your results on "11.3.0 for Mac OS X x86 (64-bit) (March 7, 2018)".
It is possible to get the data using free-form input. On a Mac Control =
(probably the same on Windows) and type in "msft p/e ratio 2000 to 2018".

Evaluation returns a TimeSeries

Converting the free-form cell to InputForm
gives the following which you can modify and evaluate.
Entity["Financial", "NASDAQ:MSFT"][
EntityProperty["Financial",
"PriceEarningsRatio",
{"Date" -> Interval[{DateObject[{2000}], DateObject[{2018}]}]}]]
There are several other financial properties that can be queried using the entity framework.
EntityProperties["Financial"] // CanonicalName
{"AdjustedClose", "AdjustedHigh", "AdjustedLow", "AdjustedOpen",
"Ask", "AskSize", "Average200Day", "Average50Day",
"AverageVolume3Month", "Bid", "BidSize", "Change", "Change200Day",
"Change50Day", "ChangeHigh52Week", "ChangeLow52Week", "CIK", "Close",
"Company", "CumulativeFractionalChange", "CumulativeReturn",
"Currency", "Dividend", "DividendPerShare", "DividendYield",
"EarningsPerShare", "EarningsYield", "EBITDA", "Exchange",
"FloatShares", "ForeignListing", "FractionalChange",
"FractionalChange200Day", "FractionalChange50Day",
"FractionalChangeHigh52Week", "FractionalChangeLow52Week",
"FundamentalCurrency", "FundFamily", "FundStyle", "High",
"High52Week", "Image", "IPODate", "Issue", "Last", "LastTradeSize",
"LatestTrade", "Low", "Low52Week", "MarketCap", "Name",
"OfficialName", "Open", "OriginalSharePrice", "Price",
"PriceEarningsRatio", "Range52Week", "RawClose", "RawHigh", "RawLow",
"RawOpen", "RawVolume", "Return", "Sector", "ShareClassDescription",
"ShortSymbol", "Symbol", "Type", "Volatility20Day",
"Volatility250Day", "Volatility50Day", "Volume", "Website"}