You're comparing frontal assault on battle hardened troops vs. potentially highly maneuvering invasion. It is somewhat like comparing Harkiv operation in the Fall 2022 vs. counteroffensive in the South in the Summer 2023.
In Kursk Russian forces can't maneuver much, they have to directly push on Ukrainians. The density of Russian and Ukrainian forces in this war - like ~500K each on the 1000km of the battle lines - is order of magnitude higher than that of the Baltic states militaries. Potential invasion in the low density situation of the Baltic states would make sense by cutting through un/low-defended areas with encircling/etc. of the more fortified areas without direct assault of them, at least initially.
In Kursk Russian forces can't maneuver much, they have to directly push on Ukrainians. The density of Russian and Ukrainian forces in this war - like ~500K each on the 1000km of the battle lines - is order of magnitude higher than that of the Baltic states militaries. Potential invasion in the low density situation of the Baltic states would make sense by cutting through un/low-defended areas with encircling/etc. of the more fortified areas without direct assault of them, at least initially.