I generally think, in my experience, that 20th century pieces are harder to perform than classical works because of the increased technical demands that are placed on the soloist. But I believe that the Haydn Trumpet Concerto is not easy to play compared to the Arutiunian and in some respects even harder. Having compared the two concerti, I found that there was surprisingly a lot in common.
I found that the Arutiunian had the following qualities:
Another new development in the Arutiunian is the blending of the
Cadenza with the general flow of the concerto by accompanying it instead of letting it be a solo bravura part. The whole tone melodic ideas and the intense rhythmic drive of the work also gives the concerto a Russian folk feel.
These are all traits from the Romantic period and having researched Russian Trumpet concerti (see appendix no.6) I can conclude that the Arutiunian is a Neo-Romantic Russian Trumpet concerto.
I might even suggest that if Haydn was alive today he may well have written a work very similar to the Arutiunian concerto.