I'm kind of failing to see how adding 'else' is trinitarian.
He is before all things.
He is before all else.
If anything, it seems to me that the alternate 'else' is anti-trinitarian, similar to adding 'other' to vs. 16. You say that the idea was to exempt Christ from creation. Leaving the text as 'he is before all things' seems to do a better job of showing him exempt from creation than saying 'all else.'
In this case it seems to be less of an agenda to prove something, and more an alternate wording, not added wording, and the alternate wording does nothing to prove anything trinitarian imo. It's interesting you read it that way. It seems like you could be saying the opposite of what you are intending to say, which would be: 'Why don't you people criticize these other translations for saying 'else' in the following verse, because it sounds less trinitarian?' Maybe if their agenda was proving something unusual and saying they are the only mouthpiece of God, and everyone better listen to their unique 'truth' or be destroyed, it would be different.
I do agree with you in your last paragraph above when you say there is no way a translator can be 100% accurate in their attempts to translate.