I've no doubt it'll remain a great help to you, even after this change. Certain evolutions do tend to come with personality changes, but they tend to be more... physically drastic.

[As someone who also trains three Gyarados, he knows that all too well.]

They can learn Toxic and Return for certain, but as nearly every Pokémon can do so that was to be expected. Brick Break is a pleasant surprise, however, especially since it covers their dark-type weakness. Flash Cannon could potentially compensate for their lack of offensive Steel-type moves at early levels, but it's sadly ill-suited to their strengths...

[Asking Cecil about TMs is not always a good idea.]