It was a bad move but the politics of Britain joining the war had everything to do with Belgium and nothing to do with the German Navy.
Yes, Jutland mattered because techically it was a German victory but the poor coordination between subs and the High Seas Fleet robbed Germany of a once-in-a-lifetime chance to totally cripple the Royal Bavy and pushed Germany into unrestricted submarine warfare.
Submarines in both World Wars had little chance to act in concert with a surface fleet once a major battle was joined. They could serve operationally as pickets, and sink damaged enemy vessels. But their slow submerged speeds, lack of sensors beyond the Mark One eyeball operating thru a periscoe, and primitive contact torpedoes all limited their battle potential.
Conventional subs were better suited for commerce raiding.