Maple Magician Shields will be more valuable in the future?

The way it is now:

1-30 1st Tier (1st job)
31-70 2nd tier (2nd Job)
70+ 3rd Tier (3rd+ Job)

So people would assume that if the job requirement levels are being lowered, then potential tiers would be as well?

3rd tier is 71+
And no, that is a ridiculous assumption.
There is no indication that potential tiers have anything to with job advancement rather than coincidence.