Evelynn ultimate should be buffed

Currently ultimate has a 250 radius AOE which is tiny compared to 550 AOE disable with 80% AP scaling or ultimate with a 1175 casting range and 80% AP Scaling as well as a 1.75 second stun. I think needs more benefits from her ultimate, as her ultimate is really weak even in late game, as it is rare to have more than 2 champions in a 250 radius to proc her shield effectively which is a measely 600 HP shield for hitting two champions. As for the damage aspect it currently scales at MAGIC DAMAGE 15 / 20 / 25% (+ 1% per 100 AP) of enemies' current health SLOW: 30 / 50 / 70% SHIELD STRENGTH PER CHAMPION HIT: 150 / 225 / 300

So to put this into numbers let's say she has 3 points in her ultimate and has 300 AP. This means she does 25% + (300 AP / 100AP = 3%) So 28% of enemies current health. Let's say the enemy has 2000 health. 2000 x 0.28 = 560 Damage and a shield of 150 HP. That is admittedly very little damage from her ultimate as Amumu does 350 + 240 = 590 AP Damage which snares and he has an ability which would do 6% of enemies health in dmg every second and he has a stun.

Now I am not saying Evelynn is weak in any way, I am just saying you can afford to buff her some more and make her a better tank that doesn't need damage to deal damage. She's in a bad spot right now as if you build too much AP/AD you're squishy and get blown up. If you build too tanky you do little dmg late game and an ultimate that can't hit enough people to get a large enough shield to absorb damage. Now before people say I think she's weak , no I am not saying that . As she has great ganks with her passive and considerable burst early game. She can snowball into an early victory and she is good enough late game but she doesn't compare to Sejuani who can deal 15% of enemies current health every 7 seconds with max skills into it and with 300 AP. Also she can go full tank and still provide ridiculous amounts of cc + damage as well as a long ranged stun which doesn't require her to get into the enemy team at all. If you read so far thanks and please tell me what you think.