If their damage is based on HP or Defence then you build HP or Defence. Stacking Attack will do nothing for those champions.

There is still a reason to take better weapons. The main stat, flat atk, is useless for def or hp based champs. But the substats from 6* weapons are better than the substats of lower tiers. The weapon is not first priority, of course.

Also, since it's not always obvious - the reason that higher-quality gear is better is because the substats are built-in. This gives you two main advantages - first, you get to make sure that the substats are the ones you're looking for. But also, since they start on the gear, ultimately you'll have higher substats with the epic/legendary items.

Thanks Peeps.  That is about how I have been proceeding, but as far as getting 6 star gear, THAT is out of my range of possibility, as I cannot advance in the Great Hall enough to be able to compete at those levels.

Great Hall progress has NO IMPACT on completing level 20 dungeons.  Absolutely none.

We had a clan member who was at Dragon 13 when joined with only 5 (maybe 4) level 60 champs.  Leveled one additional champ to level 60 and completed Dragon20 in a week.  They had never advanced out of bronze 1 in arena.

This is where the "I think this is a Hero Collection game" people fail.

Focusing on few, and building strong champs is how you make progress.  The more money you spent on shards, the more you likely hurt your progress.  Because you have spent all your resources leveling too many champs when you don't have enough GOOD ARTIFACTS for even a few.