[@ManyThings] Okay! So a few things we need to tackle here.

I'd lower either strength or agility by one rank.

Theseus has not ALWAYS been seen as the Son of Poseidon, most stories called him the son of Aegeus which you chose to represent with a -, but I think we should knock that down to C to keep it realistic. 

I also do not understand why riding is A+ when his story, for the most part, is not about riding/sailing, it is about everything between. If that is the case, and you wish to go with the ship as his main mount, you'd need the "Voyager of the Storm" skill and you could drop riding altogether. 

I still believe he qualifies as a rider and that the sheet works, but I think a lot of the stats are elevated to an unrealistic and unfair level given his story. 

The road to Athens is fine, it makes a lot of sense!

The affection of the Sea God feels more like a Noble Phantasm and less like a skill, I will ask that you remove that all together, or replace a current NP with that, even if it is an altered version.

Bravery is fine.

I think you should choose between the bull or the thread about these Noble Phantasms. Yes, some servants have Three Noble Phantasms but the most common amount is only having one! That being said, I'm not opposed to three, I just don't think BOTH of those are worth keeping. If it were me, and you truly want to run with the Poseidon aspect of his story, then I would get rid of both of those and do the affection of the sea god as an NP, and expand on that. 

If you want the bull to be his mount and not the ship, then that changes a lot of stuff as well! So I'd pick the ship or the bull, but the ship is probably the more solid option.