It really doesn't matter when the WBC is held. By definition, WBC games played by major-league players are innings that do not contribute to their teams' success, that are played outside the terms of the very attractive contracts these players command. Arguably, no player on a 40-man roster should participate.
Prospects — kids not on 40-man rosters —could participate, if the WBC were scheduled sometime during the regular minor league developmental cycle. Players would be fully in playing condition, and the innings would substitute for innings the players would otherwise play in the minor leagues.
But the WBC is an exhibition, a spectacle. Players on 6-figure to 9-figure contracts should not be risking their health participating in such a spectacle, any more than they should be playing football in the off-season. I mean, can you imagine J.T. Realmuto playing in the WBC, and blowing out a knee in a non-Phillies game? Stuff happens, but it's just nuts to go looking for it.