Yes, it could be a valuable addition
He can easily 'deserve' this tool as the Leader of his faction, the lore indeed tells us that the Dwarves are obviously overall more resistant against Magic and stronger than Humans, and in BOTFA we clearly saw the display of Dáin's physical Strength in the heat of the Battle.
However, it's crucial that this hypothetical knock back effect remains very 'moderate'; 1-2 units involved, for example.
I agree with you my friend!The effect is well deserved and as you say we saw his Raw brute Strentgh not to mention Dwalin lifting big/huge rock which nor Human can lift with ease and Dain is may be stronger than him!
BUT I do agree that his Are DMG and Knocback DMG should be with middle strentgh not too much to make him too OP but just to display his Prowess in Battle and Physical Strentgh!
While it is certainly lorewise a well placed buff / change, I don't really see the purpose strictly gameplay-wise: Of course Dain is a strong warrior, but ingame he has the role of a support (both Dains), therefore at least AoE-damage isn't really at place. I could however agree or support the idea of giving him a small knockback against troups without damaging them (exactly like Boromir) because this form of knockback is practically a cc-effect which supports your own troups by disrupting the enemy. Also this would be a way of not making this feature too dominant or strong as dwarvens already have very strong heroes.
What I like however is the small balancing issue between Iron Hills, Erebor and Ered Luin as with your idea Iron Hills and Erebor would have easier access to knockback. On the other hand: This feature would propably be of better use in the hands of Thorin Stonehelm (is this his english name?), so I am not certain about your proposal, eventhough I like parts of it.
Greetings
Melkor Bauglir
Thank you for the polite and reasonable reply,I respect your opinion and the facts you stated!
Now I think Lord Dain as he is in his Prime should get Both Area and Knockback but with moderate strentgh as Walkure said,while in Erebor as King Dain is already quite old he can have only small knocback(2 units) simillar to Boromir to represent his old age,while I like the idea of his son Thorin III Stonehelm to get at least Are DMG or Konockback or both since he is in his prime by then and is supposed to be rather good Warrior probably Dwalin Level!
So basically I think a moderate Knocback and Are DMG for Lord Dain and only Knockback for King Dain OR Knockback and Are DMG for his Son Thorin III Stonehelm which as Melkor said which will good too since by then Thorin is supposed to be well versed and strong warrior!
Or enormous magical powers
And yes my friend the Strong Magic users deserve it even more to a degree and Galadriel I hope will have too!
She most ceratinly Knocbacked quite good that Guard in Dol Guldur XDXD XD