Typically, whenever I recommend the release order for playing these games, it's not normally out of a sense of "you won't understand what's going on", Because in all but extreme cases, that's false. It's easy to just ignore words you don't understand, and as long as you start at the beginning of an arc, you'll at the very least understand that arc's story. There'll be references you miss, some characters you might not be as emotionally invested in, but if your goal is to just play that arc, a bit more investment isn't worth hundreds of hours of JRPG.
...Even if ____ from a previous trails game shows up at some point and goes "WOW THIS REMINDS ME OF WHEN I ____ IN THE LOCATION ____", thus making you feel very alienated.
Really the real reasons to care are that
A) all the Trails games (I've played) are good, and I'd argue the best game isn't *that* much better than the worst one
B) Once you're in to Trails (read: reached the end of a game and realised that all the build up is in fact going somewhere), there's not much reason to not go in release order as much as possible.
and
C) Previous games will suffer more if you've gotten used to the QoL changes of future games, and if you've already been spoiled on the general plot beats.
If someone wants to start with CS3? Go ahead, why not. They should at least play CS1 and CS2, and ideally they should play Sky too, and if they hate fun they'll wait along with me for the Crossbell fantranslations to be in a good state. And I'll let them know this so that they can make an informed decision. But hey, I don't care. They'll realise their mistake later figure out what they want to do eventually. They can't say they weren't informed. And if they have fun, that's good!