I would say Keldeo is also a threat to voltturn, as it can't exactly switch in but it has massively powerful attacks that nobody on a voltturn team wants to take (hydro pump, secret sword, even icy wind can kill momentum). It fits the description of "powerful choiced attacker" better than pretty much everything else on the special side. I'd also mention Landorus a bit less, as it's more commonly used as a special attacker.
Part of the GP team, message
me for a check!
Sharpen your skills as a GP checker in the GRAMMAR DOJO!