It's not an exaggeration, it literally (nearly) triples your \fTP. It's the single biggest ws damage increase you can give yourself after making a Tizona. If you want to see the difference, just start holding TP to 2000 before weaponskilling.
Even assuming best case scenario for you claim (which is lowest possible TP thresholds with moonshade and only comparing 1st hit without 2nd, offhand and AM3/MA proc)
1250TP: ~5.195 fTP
2250TP: ~10.09 fTP
Its not even doubling it like I said. In reality you dont WS at 1000TP tho, but usually on avg at least at 1150 without samurai roll and much more with samurai roll. In reality you also have 2nd hit and AM3/MA proc chance. First hit is obviously dominant here, but even with 60%WSD, we are talking about:
5.195 * 1.6 + 1.8 = 10.112
vs
10.09 * 1.6 + 1.8 = 17.944
Thats around x1.775 increase, not x3.
If I would like to be even more into details, I would calculate drop from damage and accuracy on offhand hit, AM proc on offhand hits and additional damage from STR and QA3% on something like Zantetsuken, then I would take real TP avg and I would probably end up with something like x1.5
Like I said, stick to facts.
EDIT:
1000 TP: 3.796875
2000 TP: 9.390625
I said fTP, not damage.
This is super unreal, because its assuming you dont have moonshade, you only hit with 1st hit and miss with 2nd, offhand and possible AM3/MA procs and lastly always WS at 1000, which is super far from reality. Even then tho 9.390625 / 3.796875 is ~2.477, so its still closer to 2 than 3 lol.
EDIT2:
Regardless though, it's generally worth using.
This I can agree with :) Afaik I was the first person suggesting Thibron offhand for Tizona and trying to justify that idea with both math and practical numbers (at least on this forum). So yeah I am a huge fan of Thibron, but I will be boring at this point.. lets stick to facts XD