Earlier quoted context omitted.
Your method is easily exploited by a malicious miner. Clocks across the network are going to have some inherent amount of skew. By forcing blocks to have incrementing timestamps and also by refusing to accept blocks in the future, you have made it easy for me as a miner to commit abuse. Instead of picking the exact current time, I will pick a time that is as far in the future as the network allows (taking full advant…
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 d…
There are consequences to having blocks that are permanently set forwards beyond a one-time difficulty decrease of 0.6%.