Finding it difficult to intuitively compare units based on their stat cards

So I'm having a hard time wrapping my head around how to effectively compare units against one another, especially when I'm relatively unfamiliar with the units.

I have a pretty good understanding of what the different stats and bonuses mean- it's the practical application that trips me up

For example, let's say unit A has 30 melee attack and 100 weapon strength and unit B has 28 melee attack and 90 weapon strength and all other stats are equal. On the surface unit A is obviously a little superior... but now let's say unit A is composed of 20 soldiers and unit B has 40. Since the stats are on a per model basis, wouldn't this mean that B is actually the better unit since 40 models with 28 attack are capable of outputting damage at a greater rate than 20 models with 30 attack?

Also, is attack speed/rate of attack a thing? Anecdotally it seems some units seem to make their actual attacks at a more frequent rate than others. If so, is this already factored into the overall melee attack and/or weapon strength stat? Otherwise two units that seem comparable with very similar attack and weapon strength stats would actually be markedly different if one attacks 30 times a minute and the other attacks 20 times per minute.

It just seems like there are a lot of mechanics at play that make it difficult to assess the strength or relative value of a unit simply based on its stat card.