Are the Tactic Skills Worth it?

Personally, I find the tactic skills to be very useful. One of my teams consist of a blade tome Nino, with Seigbert running Attack Tactic in the C slot and Defense Tactic in the seal slot. With a Speed/Res rally in his support slot, he buffs all of Nino's abilities in a turn I wouldn't be using him to attack.

That tangent aside, I really do think a tactic skill is good for your team, given that you stick to the requirement. The 2 range on the buff is amazing. I'd recommend a tactic skill on your team.

Edit: Thinking about it though, the units you get the skills from are very valuable, especially Siegbert for Attack Tactic. I'm not 100% on L'arachel though, I never used her myself, so just make sure you won't need these units in the future.

Tactics skills are definitely really strong, but it is admittedly expensive. You could play around with res tactic pretty easily though if you have some spare 4* l'arachel

It's easiest to play around with def tactic since it's on the free VL!Ike as well as one of the last tempest trial rewards.

If you're planning on merging your dragon team, I'd look for some goad dragons and ward dragons, or hone/fortify would be good too because they tend to have enough HP to be relatively panic resistant (not 100%, though. I've seen armours with 53+HP in arena and I'm only scoring max 704)

Tactic skills are very good, though, if you're doing mixed teams. The only buff I think that has greater power is goad fliers, because it's available, and +4/+4, and fliers are so mobile and goad is currently immune to any enemy interference. Hone fliers, hone cavalry, and hone armour are pretty powerful but a bit more difficult to position for (also subject to panic, which affects mainly the first two); tactics will activate more easily if you have a mixed team.

I do find tactics relatively inferior in grand conquests because it's so easy to have 3 of a movement type. The other issue with tactics is that it can be difficult to plan a team so that everybody receives all the tactics that they most need. It's possible to plan the team composition and the C and S slots so that everybody gets buffed in their most important stats, but usually when I've tried this it's very difficult. The imminent release of the res tactic seal should help, but it's still not easy. In any mixed team you might end up with a character giving spd tactic who could use the extra speed himself/herself; it will almost certainly be the case on a dragon team because dragons like all four of their stats, so you'll have to pick and choose and really understand the roles clearly in your own mind because the stats themselves aren't necessarily going to suggest anything obvious.