I cannot confirm how bright the E12R will be but I think the 519a has a lot of benefits because it has really nice overall tint (much nicer than lh351d in general), and also have a lower V_fwd compared to lh351d or sst20 or xpl-hi. The lumen per watt of the 519a is maybe not quite as good as xpl hi, which means on regulated mode it may not be as bright, but on turbo in the same flashlight it should be brighter than xpl hi.
Also the optic has a lot to do with how bright it looks. The e12r optic is a bit more floody, so the hotspot will not look as bright and it may look less impressive even if there are more lumens. Also keep in mind the e12r driver has a few more components inside such as reverse polarity protection fet and current sense resistor, so the output on turbo may be lower than other simpler flashlights, with the benefit that it can probably run in turbo for longer (e.g. 1 minute instead of 15 seconds). It will also help if you buy a really high drain battery like molicel 42 or 45 if you want the max turbo.
Personally I think turbo on fet is a gimmick and I much prefer sustained good long runtimes at high brightness. The 519a is the best high cri option right now.
1lumen did a test with e12r and nichia 219b lumen and was 6564 lumens on turbo. I also found this page that SKV89 did a test on e12r and he later comment about e07. Both using 219b leds, the e12r measures 4319 lumens and the e07 was 3000 lumens with his lumen tube which he says may read a bit lower than usual. Fireflies E12R, NOV-MU, T9R, T1R prototype test results. I am not surprised about the big difference in numbers because fet mode is unregulated and depends a lot on many conditions. For example, how clean is the screw thread? How warm is your battery and what voltage did you charge it to? A warm molicel 42 charged to 4.25V will be much power powerful (more than 2x or 3x or even higher) on turbo compared to a cold samsung 50e charged to 4.15V.