I think in general fighters should be more active. But it depends upon the fighters age and level of opposition. Older fighters bodies will have accumulated some wear and tear so they would likely pick up more injuries fighting 6 times per year. Better for older fighters to have fewer fights so they prolong their careers.
Mike Tyson in his younger years, I think it was 1986 or 87 had over 10 fights in a year. That same year included a heavyweight title fight against Berbick if I recall correctly. However, Tyson probably did more work in warm up for those fights than he did in those actual fights! Parkers career path is almost a throwback to the old school where boxers fought a lot more frequently. Like I said before, compared to Joshua, Parker is; Younger by 2 years Has had 5 more fights And started his career AFTER Joshua had started his I think some boxers should keep a lot more busier.