You're comparing apples to oranges. The Deathwatch specialise in covert anti-xeno operations. Things like assassination, asset recovery. They are the spec ops of Space Marines. It is counter-productive for them to have unpainted silver armour like the Grey Knights.

Also, no, the Grey Knights do not boast. They have some of the best wargear because it is specialised. They need that specialised wargear to be as effective as they are. Honestly, I think you have a wrong understanding of what the word 'boast' means. Based on your logic, Terminators in a regular Astartes Chapter are boasting simply by wearing better armour than their brothers in the normal battle companies.