Maybe it's just a stat avatar to you, but obviously from the responses most people here seem to agree that they mean more to them than that. Obviously we'll all be using new gear and weapons and there will most likely be a new class or two, but the things our guardians have accomplished through the first 3 years should still mean something and we should be able to progress with the characters we love if we want.
Also they could bring forward D1 gear in spirit at least through transmog if they wanted.
The fact is that anyone who doesn't want to continue and wants a fresh start will have that option regardless so those who want to continue with their current Guardians have zero impact on your experience.
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The accomplishments would be reflected in the game world anyway, they have not done anything to make any of the guardians feel unique or accomplish anything. For example when TTK came out it didn't matter whether someone had killed Crota or not, the game world moved on as if they had. So any accomplishments your guardians COULD have done, whether they actually had or not, will be reflected as being completed in the story. So they really are just stat avatars. It's more important that the next game isn't held back by the previous game in any way.