Javelin is a bit of an outlier in the Olympics in that throws today are nowhere near the records, even after the changes discussed in the article. The winning throw this year was 87.58m, with only one other competitor managing even 86m. The world record, dating from 1996, is 98.48m , a full 10 meters and then some longer. Germany's Vetter, the one modern javelin thrower who has come within striking distance of that (…
Looking at the list of furthest throws[1] this doesn't really seem that obvious at all.
The top two are quite large outliers, with a 4 metre gap to #3, and people in general don't seem to have been throwing much further in the past. Indeed, the difference between #1 and #25 is almost 10 metres, or 10% of the record. That's quite the difference!
Johannes Vetter seems to be in the same league as Jan Železný; Vetter is 28, Železný established his record at the age of 30. It's entirely possible that Vetter will manage to break the record in the future.
So either both Železný and Vetter are exceptionally talented athletes in their field, or they're both doped to the gills without being caught. It's not like there wasn't any attention to this in the past, see e.g. [2] from 1989. There sure is more attention to this now and I suppose it's possible that Železný used doping, but that Vetter exists in the same league as Železný demonstrates that Železný didn't have to be a doping user to be so good at it.
So in short: it's not all that obvious to me looking at the data. It's not like cycling/Tour de France with a long history of doping use (which is partly, I suspect, because what's being asked of riders borders on the inhuman).
[1]: https://en.wikipedia.org/wiki/Javelin_throw#All-time_top_25_...
[2]: https://www.washingtonpost.com/archive/sports/1989/06/18/in-...