Read your last sentence.
Nelson played nine games for Leicester last season. That appears to me that he filled in when required, not a first choice.
He may well be an U20 player and represented his country.
Brown is a full international player, has played at Championship level and played a full season in a team that gained promotion.
He has amassed many games at League 1 and Championship level. He's now regarded as an experienced pro.
Nelson has 9 senior games with Leicester and two loans to league 2 teams.
The experts agree he's got good potential to become a decent player.
That's why we signed him on loan.
If anyone thinks he's going to dislodge Brown from CB in a straight swop they need to give their head a wobble.