Kayle Pre-nerf was building max Attack Speed. Berserk + Nashor's + Rageblade + Runaan's + Wits +30% from runes
So you include Rageblade but you leave out the Runaan's procs in a teamfight setting. That's 1120 on two side targets.
The reality is, between 10 Autos with fervor Kayle got 1120 damage in Physical, 560 Magic damage (Rageblade Converts it to magic), 1120 on two side targets.
280 Physical Damage + 140 Magical (Phantom hit) + 280 x2 (Side Targets) 840 Physical damage, 140 Magic damage (average) = 980. About a thousand DPS from old Fervor.
The best case scenario for new fervor is MUCH less, considering it takes longer to stack and doesn't synergize with rageblade or runaan's. For simplicity, going to assume 2.5 attack speed for a comparison.
600 Physical Damage, 240 Magic Damage. (Assuming phantom hit, you get an extra 120 from it) Assuming Runaan's, you have .4 Crit 840 + 260 best case for single target. 210 + 240 Magic damage per side targets.
150 Damage + 60 (+ 30 Phantom) and 52.5 + 60 to side targets.
150 + 90 Magic damage, and 52 + 60
With those numbers, the DPS is significantly lower over time. We can do this again assuming 100% critical, giving the new fervor a better shot. (Even though Kayle doesn't like Critical)
1,500 Damage, 360 Magic damage. With Runaan's, side hits will do 375 + 240
375 + 90 , 93.75 + 60
Best case scenario,
280 + 140, 280 (Old Fervor)
375 + 90, 93.75 + 60 (New, Best Case with 100% crit, and IE)
150 + 90, 52 + 60 (Same build as before)
It would be considerably better if it stacked with Abilities again, and had 8 max stacks. It's just outclassed even further in practice. TLD or SRS.
Considering Rylai's, It's definitely a situational and playstyle dependant item. A number of mages came out of the MYMU and made great use of it. Though, you can't deny that Kayle didn't make extremely good use out of it with the Runaan's + Rylai's synergy. It's a nerf to her teamfight control, and pick potential. I think it's really dependant on where you play her. I think when you look at it, it's a pretty okay buff for Mid Kayle, and a nerf to her Top.