Panasonic FZ300 has a 12.0MP 1/2.3" (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Venus Engine processor. On the other hand, Panasonic G7 has a 16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Below you can see the FZ300 and G7 sensor size comparison.
As seen above, Panasonic G7 has a 8.0x Larger sensor area than Panasonic FZ300. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.