Since this question is still up, I'll give some of my observations here.
Stat-wise, Grapploct is rather lackluster, but it's not dismally bad. The poor Speed is not that big a deal, and could even be a boon specially if you decided to use it in a Trick Room team. The rest of its stats are well rounded, so it can actually be surprisingly effective, specially if you catch your opponent off guard.
Movepool: Grapploct has a pretty terrible movepool, but again, not atrocious. It has Liquidation, Octolock, Superpower, Sucker Punch, Topsy Turvy, and Circle Throw, all of which are decent moves that help in chip damage and utility.
A great example of Grapploct absolutely demolishing an opponent team would be if it was against a Pokemon that cannot damage it via Toxic/Seismic Toss, and then using Octolock to trap them while you Bulk Up a few times before gaining an edge over the opponent. Do note that this is more of a gimmick that could work under optimal circumstances, but doesn't guarantee anything.
I think Grapploct was designed to play a support role rather than shine as an attacker or sweeper. That said, I feel an Assualt Vest set with full investment in Attack and HP can make it a bulky tank which can wear down the enemy, specially with Drain Punch.
But that's not all. Personally I feel Grapploct can really shine in doubles, and here's why:
- Octolock can be a surprise trap that can wear down opponent walls while your own Sweepers take the opportunity to boost and sweep.
- Topsy Turvy can be super useful if your partner Pokemon uses Draco Meteor/Leaf Storm/ Overheat, etc.
- Just for fun, you can use Octolock on your own Partner Pokemon which has Contrary, which keeps getting bulkier, and can't be phased out.
- As mentioned above it can help out massively in Trick Room teams with its low health.
All in all, I'd say that while Grapploct isn't the next Landorus T or Tapu Lele, it's not utterly garbage either, but you're better off using another Pokemon in its slot unless you want to win through some funny Doubles shenanigans. Grapploct doesn't stand out as a competitive Pokemon, but it needn't be written off.
Finally, as far as in-game play goes, I'd say it's actually quite good. The low speed is easily fixed by overlevelling, and it can simply click Liquidation and Drain Punch to victory. If you need a Fighting type for your Sw/Sh playthrough and don't have access to the others, this isn't a bad choice by any means.