It is true that his attire was minimalistic compared to when he's in Nazarick.

I guess he feels that's enough to beat Shalltear.
It partly explains Cocytus probabilities, that were a bit low for Ains. 30% is already too much of a gamble for such a small objective, justifiying getting some help if it was his maximum capacities...


But it isn't the case. He's been there with lots of handicaps.
I guess it serves several purposes:
He does not disclose too much about the extent of his capabilities to any spies... Or even his underlings.
He shows everyone he's boss, particularly his underlings...