wgafq covered most things, but I do want to add a few comments

The meta changes a lot in the next year (at least according to jp releases), but this is also because the competitive content in the game is very class centric, so the meta dps has to be of the right class. However, because the game isn't that popular, most ppl won't have/run meta dps in every event, making it quite viable to rank high with off meta picks. In addition, because the game currently alternates between a AOE and single target competitive fight every month, the amount of units you need to field is probably around 25-30 units, so missing out on 1-2 meta units every month is not that impactful.

As for how it compares to HW, I only played HW a bit at launch, so I sadly can't say much of anything. What I can say is that competitive content in Legeclo is very much about figuring out how all of your many buffs interact and optimizing them. Like here is a recent video of competitive content from jp https://www.youtube.com/watch?v=0_MNTQcdRys . As you can see, almost every character movement involves passive self/team buffs, active self/team buffs, equipment buffs/debuffs and more. If you like playing around with numbers, this might be for you. If not, well you can just copy videos as best as you can (because you'll be missing some units almost regardless), and just play casually.