Riot vs Time spent in game vs Skill-based game

I'm confused here. Does Riot want us to spend more time in game or (for some reason) don't want us to because a large volume of players (just hanging around) will impact the servers?

Played this game since beta. I have 3 accounts on 3 servers and frankly, I've only spent about $60 on the game since the beginning. I only play for first wins these days. I would play more (or pay more) but I feel the reward isn't worth time/money spent. Arguably, more experience does not mean u're better at the game since it's a skill-based game. I know fun should be derived from the game itself. But more experience should count for something? More than rare Summoner Icons or super rare skins?

While Diablo3 has the paragon system and Marvel Heroes has Omega system... those are ARPGs and we can't expect the same power-creep system in LoL... But LoL only has the Rune and Rank system going for Riot... And if u're not inclined towards the competitive, u only have the fricking Rune System ;D

I thought with the mastery system there would be better incentive to play the game more. I've accumulated a bunch of mastery points on some champs I enjoy playing. But no... mastery 6 and 7 takes a couple of games with S rating and a bunch of shards. Even then u get nothing to show that u've invested into the champ except for an emote. =/

There's literally no incentive to play this game for a long time. After 5 years and u hit your own "skill cap" of sort, there's nothing going for this game for veteran players. I know you're catering for new/casual players. But Experience with a game should count for something. It does nothing for this game except a few rare Summoner skins or icons to show.