Negative, this is not true. By my information there's not a single application around that allows to handle/decrease kernel wakelocks. If you're unhappy with specific kernel wakelocks I only see two changes: To either change the kernel and try a different one, or to manipulate the environment in that the device is working. Example: As I stated here I was able to decrease the mdm_...-wakelock by manipulating my WiFi setup.
Boeffla Config App (as nearly all other kernel configuration applications do e.g. Kernel Adiutor (KA), 3C Toolbox, AGNi control; just their GUIs are different) allows to select specific governors that come with the respective kernel, to select profiles that come with the respective governor, to change max and min frequencies for the CPU, to change the frequency "band" for GPU, to manipulate the voltage for CPU and GPU, and much more. Boeffla Config App (KA doesn't) gives you the possibility to use presets.
We all have different expectations and requirements how our devices are supposed to behave. We all use the same device absolutely differently and in different configurations. For this reason, it's absolutely normal that my i9305 might have a higher (or lower, whatever) battery drainage than your i9305. Saying that, no, I didn't tweak my kernel. My experiences with tweaking tools like LSpeed or Gov Tuner Project (if interested search XDA) are poor. I didn't achieve less drainage with them, just the opposite. And I didn't wonder as these tools do not consider my expectations, requirements, utilisation of my device and its configuration. For this reason, I refrain and are going to refrain from any further use of these tools.
No, I didn't tweak the kernel but I modified its settings to my personal requirements - and it was a long way to go, actually most of the time by try and error. If I have to guess it took me more than half a year to find my current settings, and it included crashes, unintended reboots, frozen screens, black screens etc. Occasionally, I "published" my settings and experiences in the RR thread (both sections), on some kernel threads (e.g. the AGNi thread from my former RR v5.7.x times), or in one of my own threads. A search might bring you there; however, I firmly believe you have to find your own preferences but while trying, always ensure you have a current Nandroid backup (in the past, there were times when I went into TWRP daily to take a backup).
I've no experiences with LOS i.e. can't comment. But in RR settings, you'll find the section "performance" (just above "about the phone") that takes you into KA (if installed or not frozen like on my device). And as stated above, KA allows you to modify the kernek settings including the governor profiles; however, there aren't any profiles like the tweaking tools offer and as you've mentioned.RR is a great rom, but I'm having seriously drain issues... in LOS 14.1 u can set the battery Performance profile
to power save, balance or performance, this section seems to be missing from the RR rom. I found using balance profile on LOS 14.1, the battery has dramatically improved.