Legacy Snorlax Lick Body Slam

See this question all the time. I feel like u should keep it. Even if defending movesets matter again, the only one that mattered really was Blissey. All other Pokémon are easily beatable. Lick body slam could be an amazing PvP moveset so I'd keep it for that reason.

I would keep lick for now. You say you may not use him in raids. Unless you have a great number of other option this Lax could carry his weight in a raid. Whatever you decide you have a beastly Snorlax. Just don't accidebtly use a charge one!

3000+ CP mons don't get punished with the new system; they get favored. Their motivation erodes faster, so that it is depleted after about eight hours or so, which is exactly what you want. That's about enough to collect a day's maximum free coins. It doesn't really do you any good to have a mon sitting in a gym longer than that.

I wouldn't be in a hurry to change the fast move, but if you had several of them, I'd consider making the change. As for zen headbutt becoming a legacy move, I don't think they would do that without adding another at least equally good defensive fast move, such as confusion or extrasensory. But there is no way to really know for sure what changes will be made. The only certainty is that there will be changes over time.

I would just keep it as it is for attacking gyms.

No, just leave him like that and hope niantic will make 3k pokemons useful once again or for future usage for put in gyms, use it as attacker or just leave it if want to get kicked fast from the gym

but dont invest in trying to get good defenders for gyms, defender meta is gone

I would do it. I use my ZH/BS for raids and it performs fairly well against mon weak to psychic. Also, if I haven't already gotten my coins for the day, I put him in a gym and hope he stays there until the next day.
It comes down to: 1) What do you want to use him for? And 2) What are your other options for the TM?

i use my l/bs as backup for bosses, it still deals decent damage.