I would say he probably could beat the current Guyot, in a one v one combat.
Guyot looks like he has lost a lot of his capabilities, and relies heavily on the Unus for any actions he takes. Physically, I assume he is still a beast, and could go toe to toe with a Guyver or better ( After all, he matched Guyver 3 in human form originally), and is probably pretty durable. But that is likely it.
But considering the newer abilities Aptom has? Aptom all the way. The High Frequency Spikes, particle weapons, freezing, invisibility... Aptom has so much great abilities, that even with just his HF spike, he could likely puncture Guyot's body and make short work of him with good shot combined with his invisibility.
If Guyot was using the Unus? Would be a fairer fight and would depend if he had just the 4 for his combined form, or more. Aptom has proven to be pretty crafty with his abilities in the past, so I think I'd still give it to Aptom, but it'd be a harder fight.