No, your stats in arena are the basic level 100 ones the ninja owns + initiative. The 10% thing was there for a very short time after 2.0 introduction and was removed after 1-2 months due to a ton of complaints.

In arena the combo rating of a ninja is 0, so just have the basic chance to start a combo (that's 30% i think), unless we talk about special standard attacks.

The water whip of azure fang clone is one of these special cases since have an enhanced basic chance to land and start a combo.

I've ran mei, mabui, tenten gnw, azure fang team for 6 months in arena and i can tell you you were just unlucky (and that the guy you met used a subpar set since azure fang necessarily have to run healing jutsu as standard in that setup, since a reflected acupuncture without a 2nd healing standard is very likely sure defeat). Personally speaking i think quite the opposite about mei and by experience i'm almost induced to think her chance to apply acupuncture and start a combo is, if possible, lower than the basic chance, in the sense that is artificially lowered to 15-20% to reduce the otherwise op set she owns by herself.

Every person that experienced this team in arena can tell you that took for almost granted after tenten moved and didn't start the combo that mei wouldn't start it and thanked god when this happened while instead cursed him every time the clone didn't start it in the same case :-).

About azure fang 3rd standard i can assure you there's no enhanced chance, otherwise beating some ninja exams wouldn't have required me 100+ tries when i was low level and bp :D.

I have run the team Zelgadis talks about in arena for 4 months too and i think more or less the same things he thinks.

The chance that mei standard could apply acupuncture and start a combo is so low in arena that you are really lead to think she doesn't own at all that potential feature, you basically consider the event of its application as a gift by luck, like picking up a one of a kind in a 1000 cards deck.

About Water Style - Water Whip, what's sure is that the version the clone uses have indeed a boosted chance to start a combo and apply acupuncture, very likely the chance for it to land is 90%, but about the version the Azure Fang herself ca(n us)e i'm of the same idea of Zelgadis. It's in no way higher than any other standard attack common ninjas own nor is higher than the chance to start a combo Taijutsu Attack has (1st standard). The reason why in 2.0 Monster Strenght was added to the set of Azure Fang was to give her an high chance to apply a reliable combo triggering standard attack because she missed one that worked that way without the clone.

If Water Style - Water Whip had really an enhanced chance to land acupuncture on the target and start a combo then Monster Strenght would be totally useless, since Taijutsu Attack lands more damage than Monster Strenght up to at least 4-5 stacks of reserve seal (so if you wanted damage you would select this one) and since Water Whip would have the same high chance to start a combo, but with an effect, knockdown, that could not only link directly to AF 3rd chase without the help of any specific Summon or support ninja, but also deliver acupuncture before chaos (so if you wanted to start a combo with high chance you would select the same this standard and not monster strenght). So what would be the point of Monster Strenght if Water Whip had an enhanced chance to start a combo?