They should tie RP to damage / assists somehow as well as kills. Or maybe they do already? Haven't played ranked in a long time.
They actually do reward assists now and assists have a 10 second grace window off of team damage, which is definitely charitable. Not only that but this season they bumped up the max kills/assists total from 5 to 6. And they also started placement RP payout sooner at 13th with +5 RP instead of (I think?) 10th or better.
Ranked RP costs and payouts now look like this as of Season 8:
Match Entry RP Cost and Rank RP division start total:
Bronze: Free (Starts at 0 RP)
Silver: 12 RP (Starts at 1,200 RP)
Gold: 24 RP (Starts at 2,800 RP)
Plat: 36 RP (Starts at 4,800 RP)
Diamond: 48 RP (Starts at 7,200 RP)
Masters & Apex Predator: 60 RP (Masters starts at 10,000 RP, Apex Predators are the top 750 RP total Masters)
Then there's the Kill/Assist Points (which have a sliding multiplier improved by placement) and the placement points themselves.
KP placement multiplier:
20th - 11th: 10x Kills/Assists
10th - 6th: 12x K/A
5th & 4th: 15x K/A
3rd & 2nd: 20x K/A
1st: 25x K/A
Placement points:
13th - 11th: 5 RP
10th & 9th: 10 RP
8th & 7th: 20 RP
6th & 5th: 30 RP
4th & 3rd: 40 RP
2nd: 60 RP
1st: 100 RP
So right now, a max point Diamond game will get you 202 RP. To break even/just come out positive in Diamond with kills/assists only, you'd have to get at least 5 kills/assists before being eliminated before 13th. Pure placement, you'd have to get to 2nd without any kills/assists. Half k/a, half placement, you'd have to get 3 k/a's and finish 9th or 10th.
Those above scenarios are all for
just going RP positive in Diamond, not even really increasing your RP, which would take consistent high kill/assist and placement games. And at that level, good luck lol.