We are not able to add players as a friend from Leaderboard or clan search. But we are able to add their opponents in their battle log. So we find his opponent and enter his battle log to add hım. So basically we can add every player but, Thé hard way. Just make it available straight.
Sad that I will be missing this game reach E-Sports level.
This "extrange flow" is not random
We previously had the add friend button available on all players profiles and top 10 players had hundreds of invites every day. Removing at at all was not a good option, and we decided to keep it on clan mates and opponents on the battle logs, this way we avoid spam with random invites but also allow to send them if you really want it.
We also considered other options like adding an option on settings to never get invites, but was dismissed as we really want players to be social, or automatically remove invites after 24h, but then the problem was with invites you really want to accept are disappearing too.