That is true, however, Unown has higher stats than Combee in every category apart from speed. Furthermore, Hidden Power can technically turn out to be every type (apart from Normal and Fairy in this case I believe). I will admit, though, that Unown is still of worse in regards to move(s), however, it can at least attack with a 72 base attack as opposed to 30.
Both are immune to Ground moves, Unown has 2 resistances (1/2 Fighting and Psychic), Combee has 3 (1/4 Fighting & Grass, 1/2 Bug), so that puts Unown at a disadvantage.
However, Unown has 3 weaknesses (2x Bug, Ghost, Dark) whereas Combee has 5 (2x Fire, Electric, Ice, Flying, 4x Rock), which puts Combee at a disadvantage.
Not necessarily saying one is definitely better/worse than the other but I think this shows that one can't say Unown is harder with certainty either.