Stacking is a bad idea, but the GOP would do it if they controlled both chambers of Congress and the White House. The GOP of the 1940s is not the GOP today. That political party is gone off the rails. The last time they were fiscally responsible, Eisenhower was in the White House.
The Supreme Court does need to be expanded though. It hears half the cases it did fifty years ago. While they are at it, split the Ninth Circuit. Give California its own circuit since the majority cases originate from that state.
Judging by the wikipedia page on judicial leanings[1], Roberts, Kavanaugh, and Gorusch are all fairly moderate, whereas Breyer, Kagan, and Sotomayor are (relatively) more ideological. Only Alito and Thomas are particularly conservative.
And it's not like rulings have always been one-sided. I know plenty of conservatives have their gripes with Roberts.
Democratic appointees even held all nine seats during the 40's, and Republicans didn't stack the court.
[1]https://en.wikipedia.org/wiki/Ideological_leanings_of_United...