Generally historians avoid value judgements as being out of scope (this is part of avoiding "presentism"). It's not entirely obvious what "as bad" should be interpreted as. Firstly, the monotheists you refer to would often feel that their motives were benign (saving souls) while you probably feel that their values are not relevant, but that your own value judgements are relevant. Secondly you may weigh some forms of violence (say human sacrifice, genocide) as being "worse" per head than others such as war. Thirdly, there is always the problem of mixed motives - a desire for territory, or for individual glory, may be difficult to disentangle from religious belief. When Rome or Assyria set off on a war of conquest, how much was religiously motivated?

This means that it's not entirely straightforward to frame your question. There were polytheist cultures which were very violent, and often religious arguments were used to justify war - but the war was not generally used to impose a change of belief, which may be what you are asking about. There were also several polytheist religions which required human sacrifice, in some cases on a large scale. Some of the Meso-American religions are well known for this - for instance the dedication of the Great Temple at Tenochtitlan is said to have required 4000 human sacrifices over four days.

Perhaps you could clarify some of the open points above to allow us to understand the intent of your question?