Is + 21 LP gain for 3rd place normal, below average or above average?

Depends on your rank. The higher you get the less LP you begin to gain.

That’s a pretty good amount for 3rd place. It sounds like you’re still climbing in ranked (just from what I’ve seen from your posts before on here and whatnot, also love your username bc it reminds me of Tera).

Once your mmr stabilizes, the lp gain starts being more minimal. For example, a 3rd place game for me is roughly 8-10lp.

Basically it just means the game thinks you play better than your current rank, so it’s bumping you up the ranks more towards people of a similar skill level.

I had my mind blown when I got 88 LP from a first-place after being placed was expecting the normal rift LP gain of 15-20 xD

lp gain is really wierd in this game. top 4 gets LP 1st place gets the most.