"Correct me if I am wrong, but won't the flat meplat bullets penetrate without tumbling, while the round-nose FMJ's tumble, thus decreasing penetration?"
Not necessarily. For example, while A475 GI M1911 .45 ACP 230 gr FMJ does not tend to yaw or "tumble" in tissue, the AA18 .45 ACP 185 gr +P truncated cone FMJ issued for the Mk23 Mod0 pistol did yaw, often times turning 180 degrees.