how many people killed samael the first season it was introduced? a party of 5 players required to take him down because of the way the mechanic was on first implementation. It's a lot easier to tone an uber down and make it applicable to people compared to adding a brand new perfectly balanced and scaling one. The hard part is out of the way concerning Deimoss on their end. The same goes for labyrinth, some small tweaks might put it in a better place, but all the mapping, concept, fees, etc, all that big hard work of getting it in the game is done already.
Also, bowzon has phalanx, so big single target there, but I think you didn't use it in the guide cause Marco had to point it out at the time. Unsure if you had tested and re-added it, but its a big single target with proper aiming and spellbind.
Javazon has enfilade which actually does a very large amount of damage and hits a few times in its small nova (I think there's 6 or 8 blades?). Fairy ring is not a single target-intended skill simply because of the requirement for corpses. Most people have been trying to turn it into some kind of godsend single target because of the huge buff on the Titan jav with gallowlaugh, which is cool, but not the intended purpose of the skill. If they wanted it to be single-target focused, it wouldn't require corpses. Enfilade is quite good. Javazon's big issue is a disconnect between damage types, and Ricochet is kind of meh nowadays. I think enfilade should be made back into cold damage, how it used to be, and change fairy ring/titan's jav into cold or poison so that it syncs well with a possible build and doesn't just become another big fire wdm build. Cold and poison wdm are really dead right now besides maybe deathgaze barb. Wolf druid is becoming more of a cold wdm spec, but needs some attention still.
Anyways, the current labyrinth, again as said before, isn't built as the core focus of the game. It's an added late game challenge for people to push characters and specs. it needs tweaking, yea, but 99% of the playerbase isn't going to complete it, so why would devs make it a priority vs actual class balancing and more widespread content as priority