You're right. I shouldn't have made other suggestions that aren't relevant to your post. Sorry.
I'll explain here why crouch-spamming is more complex than you're saying and is a skill that someone could master:
Depending on the weapon, you can predict when a player engaging you is about to shoot and time your crouches to make them miss.
For example, the Deagle can shoot 1.78 rounds per-second (1 round every 0.56 seconds). Knowing this, if you crouch approximately every 0.5 seconds you COULD force a miss.
Also, if you are shooting someone who is crouch-spamming, you could wait until they're standing again, and time your shot correctly to score an easy kill.
This takes some skill like bunny-hopping (with a mouse scroll bind), another skill that requires a grasp of timing you haven't mentioned in this post.
You can't just choose movement skills you dislike and ignore other movement skills that suit your playstyle (for example bunny-hopping)
I've drawn similarities between bunny-hopping and crouch-spamming. Should the stamina system affect jumping as well as crouching? Your post sounds like a biased take.
To conclude, imo adding a stamina system would only hurt the server. People should be able to move freely however annoying it is. Adapt. Have a good day George.