I don't mind trials in the leveling roulette for ARR since they are 4 man runs, not true trials. That's the problem with them and why they aren't in the trial roulette. Think about it: The trial roulette is for 8 characters, the only option to make the old ones work would be to split the pre-formed group into two groups of 4, and then have two instances formed. That's a not so small amount of work they'd have to put time into right now into a system that for the most part, is working pretty well.
The main problems that exist in the game is the organized play dungeons like going floors 101-200 in PoTD. I don't think people should be forced to do those in a fixed group anymore due to it being such an old piece of content. Socially, FFXIV's end game community is sort of about doing the latest and greatest late in the patch cycle. 101-200 for relic is more of a retro run scenario that people do at the onset of a new expansion when the latest and greatest is still coming online.