Guardian rank should be: NL (New Light), D, C, B, A, S based on:
• Campaign completion
• Exotic collection
• Nightfall records
• Dungeon/raid completions
• Etc.
Example: A rank should require at least 1 completion of each dungeon and raid. S rank should require master raid and Grandmaster nightfall completions.
Seasonal ranks should be merged with weekly seasonal challenges. Rank 1-10 will be added to your guardian rank and shown on your name tag. (I.e. A-7, B-3, or S-10). Weekly challenges would be restructured to be in ascending difficulty and remove "challenges" that are simply to finish the campaign. Instead, merge those rewards with completion of the quest line.
Additional point:
It should be possible to drop down guardian rank(s) if, for example, by the end of a season, you haven't completed the new raid/dungeon yet.