Yes, if the next block by an honest miner is very quick it will pick a timestamp of (wrong_timestamp + 1) instead of the actual time, but after a few blocks they will certainly able to use the correct time again.
But even if all miners decide to do as you say and always pick a date slightly in the future but inside the wiggle room, all that they achieve is a one-time very slight difficulty decrease, but by the next difficulty adjustment that's already lost because by then both the start date and end date of the period are offset by the same amount into the future.
It significantly increases the risk of network forks for people who don't have completely correct clocks. If a merchant has a clock that is off by 1 hour (they didn't adjust properly for daylight savings perhaps, or maybe they just have a really crappy clock), then it's possible they will not even be seeing the most recent 6 blocks, as all of them are 2 hours in the future (3 hours as seen by the merchant).
There are consequences to having blocks that are permanently set forwards beyond a one-time difficulty decrease of 0.6%.
But even if all miners decide to do as you say and always pick a date slightly in the future but inside the wiggle room, all that they achieve is a one-time very slight difficulty decrease, but by the next difficulty adjustment that's already lost because by then both the start date and end date of the period are offset by the same amount into the future.