Yeah, the depiction of Shaturghan attacking a defenseless Lavanasura doesn't look too good. But then again, in the original, Shatrughan kills Lavanasura while he is eating, after he thinks Shatrughan has been knocked unconscious. The reasoning here is the same as the one interrupting Indrajit's yagna - just as Indrajit couldn't be allowed to complete it, Lavanasura couldn't be allowed to return to get back his trishul.
One thing about the opening scene in which the spy was assassinated right in front of Lavanasura - I thought that was too brazen. Also, Lavanasura had the rishis thrown in the dungeons - why would he keep 3 of them tied to the pillar of his own temple? That looked soooo unlikely. And then, when the rishis convinced him that they had assassinated his spy, he takes the trishul out to scorch them? 😲😲😲This is unbelievable - since Lavanasura worshipped Shiva and the trishul, it's extremely unlikely that he'd have used that, when his plain sword would have achieved the same thing.
I think this spy plot could have been more interesting had the spy been killed before he met Lavanasura, and the senapati returned, w/o Lavanasura getting any whiff of it.