I agree that most of the issue is with the hitters. I did a quick search for the years 1900-1909 on SO/100AB. The highest was 1902 Socks Seybold at 9.58. The reality is that strikeouts weren't an official stat for batters during the dead ball era. I know that BR shows them for those years, but having done research myself in that era, I can say that they weren't tracked back in the day. According to BR, 1903 AL teams had between 461 and 588 Ks and the 1903 NL teams had between 381 and 628. Waddell and Mathewson each accounted for slightly more than 7% of their league Ks that year. The league averages per 600 PA were about 62 in the AL and 53 in the NL. Ollie Pickering led MLB with 75 Ks, which was 1.8% of all AL Ks that year. That would equate to roughly 385 Ks in 2019 baseball. For the period 1900-1909, every hitter's contact rate is at least .900 with a maximum of .964 by 1908 Dave Brain. Clearly, Ollie Pickering's contact rate of .910 and SO/100AB of 8.98 in 1903 aren't correct.
However, I wonder a bit about the pitchers when I see the limited Waddell results above. 1903 Waddell has K/9# of 10.47 with K/100 of 25.20. The 2019 Astros had the fewest batter Ks in the AL with 1,166, well below the AL average of 1,428, but still 7.2 K per game. In the limited sample above, Waddell averaged 5.09 K/9 against the Astros. Given that his K/9 of 8.4 was more than double the league average of 3.9 and more than 50% better than the second-place total of 5.5 by Bill Donovan, I would expect more Ks from him. Obviously, six games isn't a statistically significant sample but only in the first game did he approach the performance that I would expect against the 2019 Astros.
In the sim, there are 41 seasons in which K/9# is 10 or greater. Dazzy Vance had five, followed by Bob Feller with four. Waddell, Ryne Duren, and Nolan Ryan had two each. Feller's 21.52 in his 1936 rookie year is by far the best ever. As Ks have become more common, there have been fewer of these seasons. Since the end of WWII, there have been only 16 seasons with at least 10 K/9#. The last was by Rob Dibble in 1992. These pitchers should post astronomical K numbers against any hitters compared to the real-life average of that season. 1924 Dazzy Vance (K/9# of 15.27) should be a candidate to strike out 400 hitters if he played against 2019 major leaguers. I'm not certain that he would because the sim determines hit or out before determining a strikeout.
The second round of the WIS Championship has a theme at a $90M cap at which the team's pitchers/hitters have to fall into one of the following two buckets:
1) Pitchers > 7 K/9# and Hitters > 12 SO/100 AB, or
2) Pitchers < 3 K/9# and Hitters < 4 SO/100AB.
Rationally, I think option 1 should be the clear winner especially at a $90M cap. However, I wonder whether the dead ball pitchers are really the best answer because the high K/9 won't ever really come into play.