Waiting 3 - 5 months for what? There is no reason to wait, unless one adheres to logical fallacy, and believes that Apple has a hardware / manufacturing defect specific to the iPad mini 5 that would continue to affect other iPad mini 5 in the same product lot(s) it isn't making known to the public.
The forum member should return the iPad mini and purchase a new one. There is no logical reason to tell someone to wait.
You are free to believe what you'd like.
In the lead-up to an announcement there are manufacturing pressures to build up inventory. Depending upon the aggressiveness of the schedule, spec tolerances can be temporarily raised to meet the quotas. That can result in things like "light bleed", slightly misaligned components, etc.
Once the initial batch of units has been manufactured, the tolerances return to normal. This is why there is always a flurry of reports about manufacturing defects in the first month or so after a release, but you don't see the same rate for the remainder of the product's life (even when normalized for expected sell rates)
Except for the iPad 1 (which I pre-ordered on day-1), I generally wait 3-5 months after ANY electronic device is released and I've never encountered any of the issues that are reported here.
This is the advice I gave, people are free to take it , consider it, or discard it. The OP just posted that they returned the first unit for a second and the second unit has the same issue. I'll leave it at that.