Inaccurate fantasy KDA values?

What's the reasoning behind Assists having so much proportional value? Assists can be a cheesy stat, especially when you consider that certain champions have way higher access to cheap assists (i.e. Jarvan flag, Janna shield). To me, it's kind of silly that a support who goes 0-10-20 is worth more points than an ADC who goes 10-0-2. I feel that it would be more accurate if a death had at least the same negative value as an assist, and for a kill to be worth at least 1 more point than an assist. Such as:

Death: -.5 Assist: +.5 Kill: +1.5

or

Death: -1 Assist: +1 Kill: +2

It would also make sense to include progressive point values for a player on a killing spree. Shouldn't someone get a cool 5-or-so extra points for achieving "Legendary"?

Am I misunderstanding something here? Doesn't anyone else think that fantasy KDA values should be more punishing for deaths, less rewarding for Assists, and more compensating for kills and killing sprees?