Even if the old raids+trails weren't unsyncable it still wouldn't be relevent content. If you want a challenge just go do the level 60 stuff. This is just the sort of game XIV is, content cycles out of relevence as new stuff comes in, being able to unsync stuff is only part of that and personally running content with less than the required number of members via this feature has been some of the most fun I've had.

If you STILL want to do the 50 content as it was intended then you're gonna have to find like minded people who are willing to do the content synced with you.