“Nice to the point where you're doing disservice to your work is not nice”
There can’t be a better way to explain your predicament at work.
By the way, I did go thru’ this phase during early stages in my career for the same reason you mentioned. But now I’ve completely come out of this.
I refrain from using words like please, kindly and similar vocabulary. Yet, I keep it polite but strong. This is how I word my emails:
“I would like you to do _____”.
“Would you mind getting this info for me?”
“Wouldn’t it make sense to do it this way?”
“I believe, this approach would fetch better results. Isn’t it worthy to give a try?”
The key to overcoming the habit of being excessively nice to people lies in practicing affirmation.