Tosh said:
No evidence suggests Future Gohan can defeat Mecha Frieza. No evidence suggests Future Trunks can defeat a fully powered Mecha Frieza in seconds.
Yes, there's:
Chapter: 331 (DBZ 137), P9.1
Context: challenging Freeza and Cold
Trunks: “Come at me at full power right from the start. I’m not soft like Son Goku…”
I'm sure someone as cautious as Trunks would not encourage Freeza to go at him at full power if he did not know Mecha Freeza's strength. If he incentivated Freeza to use his full power, he most likely knew Mecha Freeza's full power. Yet he said he could take him in seconds (at least according to Viz):
Chapter: 331 (DBZ 137),
Context: challenging Freeza and Cold
Trunks: "I will bring you down in seconds. I
know it."
Freeza being fodder to Trunks is even proven when Goku stated that the Androids must be pretty monstrous
for a SSJ capable of killing Freeza in an instant to be scared of them without even bringing up the fact that Freeza wasn't at full power.