Context. The dependence of the luminosity function (LF) of cluster galaxies on the evolutionary state of the parent cluster is still an open question, in particular concerning the formation/evolution of the brightest cluster galaxies. Aims: We study the bright part of the LFs of a sample of very unrelaxed clusters ("DARC" clusters showing evidence of major, recent mergers) and compare them to a reference sample of relaxed clusters that span a comparable mass and redshift range. Methods: Our analysis is based on the SDSS DR7 photometric data of ten massive and X-ray luminous clusters (0.2 ≲ z ≲ 0.3), always considering physical radii (R200 or its fractions). We considered r' band LFs and used the color-magnitude diagrams (r' - i', r') to clean our samples to consider red and blue galaxies separately. Results: We find that DARC and relaxed clusters give similar LF parameters and blue fractions. The two samples differ in their content of bright galaxies BGs, Mr' < -22.5. Relaxed clusters have fewer BGs, in particular when considering the outer cluster region 0.5R200 < R < R200 (by a factor two). However, the cumulative light in BGs is similar for relaxed and DARC samples. Conclusions: We conclude that BGs grow in luminosity and decrease in number as the parent clusters grow hierarchically, which agrees with a BG formation by merging with other luminous galaxies.