Observe
format long g
t = complex(single(3), single(-5)), whos t
t = complex(double(3), double(-5)), whos t
t = complex(int8(3), int8(-5)), whos t
t = complex(uint64(3), uint64(5))
Complex is an attribute, not a class. If you made it a class, you would need a separate class for each different datatype that can be complex -- single, double, int8, uint8, int16, uint16, int32, uint32, int64, uint64. (Complex logical and complex char get converted to double precision.)
Meanwhile you would still need isnumeric() and issingle() and isdouble() and isinteger() to continue to work on the values. What would your inheritence hierarchy be?