I just reread that scene, and it's not quite like Shannow described it. First, Dobser walks in, and Pevara wraps him in Air and shields him, (he was caught completely off-guard and not holding the Source). She then ties off the weave of Air, but is maintaining the shield.

Then Leems and Welyn enter, and she gags them with Air and tries to shield them both, but her attempts are rebuffed. Leems wraps her in Air and tries to shield her, but she slices the shield. This surprised Leems and his weaves are released. Pevara then throws herself at him, and shields him as she slams into him.

She again attempts to shield Welyn, but he grabs her with Air and hurls her backwards. While flying toward the wall, she weaves a thread of Air and grabs him by the foot as he attempts to flee, and trips him. Androl knocks Leems and Welyn out with a cudgel, then Pevara notices that her shield hadn't locked onto Welyn. aMoL Chapter 3, page 125.

Upon reflection, the main problem I have with this fight scene is that Welyn stood around doing nothing while Pevara threw herself at Leems. If he had joined the fight instead of becoming a spectator, it should have turned out different. (There is no mention of Androl being involved channeling-wise.) The biggest factor here appears to be the element of surprise.

Later, in Chap.4, page 129, Pevara's pov says she can't maintain 3 shields, and she is fearful of tying them off, because Taim has been teaching the Asha'man how to escape a tied-off Shield.

Some of your doubts about the Asha'mans skill level have been answered: Leems and Welyn rebuffed her shield attempts, and they have been learning to escape tied-off shields. As for how strong they are, all we know is that they are full Asha'man, which is an indication of some strength, but, IIRC, rising in rank is due to training/skill. (IMO, I don't think 1 year of intense training would be comparable to being an AS for over 100 years, and a Red that has participated/practiced in tracking down male channelers to-boot)