I've read this sentiment in the forum many times in the past, but is it true?

First of all, The current block height is over 790,000 so you'd need a LOT more than 10,000 blocks to "be far longer than the main chain".

Secondly, after you've churned out 2016 blocks, in order to create valid blocks, you'd need to immediately increase your difficulty by a factor of 4, then again after the next 2016 blocks, and again after the next 2,016 blocks. Pretty quickly, you'd encounter a situation where your particular equipment can't mine blocks any faster than an average of one block every 10 minutes.  You could shut your equipment off for a few weeks to get the difficulty to come back down, but you'd burn a lot of time waiting, and then once you've spent a few days mining another 2016 blocks, the difficulty would shoot right back up again.