This work presents an evaluation of the crosstalk impact on the signal-to-noise ratio (SNR) of long-distance C and L band wavelength-division multiplexing (WDM) systems using homogeneous multicore fibers with weakly coupled cores. It is experimentally shown that the crosstalk-induced SNR penalty is independent of the transmission distance on sufficiently long uniform links. This results from the approximately linear scaling of the noise contributions from amplified spontaneous emission, fiber nonlinearity, and crosstalk with the transmission distance. The crosstalk-induced SNR penalty on C and L band WDM long distance links is experimentally evaluated, showing significant degradation of signals located towards the long edge of the L-band. Up to 3.8 dB penalty was observed on a 3866 km link, in agreement with theoretical predictions. We perform a theoretical analysis of the wavelength allocation of densely packed channels for long distance WDM systems with and without the presence of crosstalk. It is shown that these systems favor the use of relatively short transmission wavelength ranges to minimize the crosstalk impact at long wavelengths. This contrasts with systems without crosstalk, which favor the low loss wavelength region of the transmission fiber.