No one at all is forcing you to use Black Kat and Chaos everywhere, some want to play more defensively or unique playstyles such as Support Bomber which is inflicting status on everything via mist bombs.
I had one for a recent Ice Queen run after Shadow Lairs were "buffed" to Tier 4, it was a lifesaver all around with a combined Fire+Sleep+Poison thawing Ice Cubes and shutting down Silkwings which were healing for 200+ HP a tick

In fact, i refuse to use Black Kat/Chaos at all in Shadow Lairs themselves, even before they got "buffed" to Tier 4. I never chance with them being the hardest content, even if i did have top tier experience.
Don't go to them often as it is.
I made unique loadouts for each one, with a rough example of Sacred Snakebite Shade/Sacred Grizzly Pathfinder/Grey Feather+Seerus/Divine respectively in terms of armor.

The problem as i see it is that with people being so experienced now that they can handle most areas with no issues, as they have the experience and know how to exactly fight enemies in groups, along with their spawn points to kill them on the spot. One example is for Wolver/Devilites, their dodges have a cooldown of 3 seconds after use, which you can abuse by baiting it out. With practice even Riftlocker can become useful by doing this.

Another example is Devilites can only attack every 3 seconds with their throws, however this cooldown is not shared with an Overtimer's melee attack, which has no cooldown and it's separate from their throws.
Basically once you interrupt a Devilite in melee, they're usually toast to take out unless it's an Overtimer.
I would back up if they try to melee instead of trying to shield/interrupt it, as not only does it come out fast enough to stop most sword combos, but attacks that can flinch will only interrupt it.
Their throw attacks sets their flinch resistance to pretty much zero so they can be interrupted by pretty much anything, the same applies to some other attacks such as Zombie's breath, Thwackers throwing their axe, or Wolvers barking.

When it comes to Shadow Lairs being "buffed" now to Tier 4, in my opinion true teamwork and lots of crowd control is a must now to not die, or at least have low death counts.
It's to a point now that you could have max out everything and be rich, Black Kat and Mixmaster alike, it's not going to save you against these beefy enemies as we are too used to enemies dying far too quickly in normal levels for them to do any serious damage.
With them now having raid-like HP to actually be a threat now, even the most simple of enemies such as Mini-Slimes can ruin you day if given the chance.
This also effectively makes Trojans/Almire Guards/Giant Lichens true "Mini-bosses" and can be considered the highest threat, and should be dragged away from your teammates and fought 1v1 if possible.

I used 8 Sparks of Life during that Ice Queen run as mentioned, despite only being my 3rd ever trip into that Shadow Lair, 1st if counting Tier 4 "buff". We were all nervous, it felt like going through old Shadow Lairs again with high stakes where energy was the only way to revive and Sparks of Life didn't exist.
It forced me to play defensively for the first time in like years, fully taking advantage of how enemy AI works and being aware of my surroundings full time.
One example is distraction, as i deliberately made sure i had aggro of some enemies such as Poly turrets and Lumbers, making sure they're only targeting me and not my teammates, while making sure Poly turrets were faced away so my teammates didn't randomly get sniped.
Enemies target players based on who dealt the most damage to them, this is exactly what i did by making sure i had the most damage on them, dashing can mess this up but with the coordination we had it rarely was an issue.
This overall allowed my teammates to deal with the rest of the types which were lesser threats, we did however still had moments where things hit the fan such as the final arena. (3 Giant Lichens at the same time was truly chaotic) We did a similar tactic for Ice Queen where she only went for me while everyone else kept minions under control.

I probably went super off-topic here, so i apologize.
Overall this is why in my opinion Shadow Lairs are good now, but i agree with most of the complaints so far with them and wouldn't mind such changes.
"Payout not good enough!" "Rewards not worth the trouble!" "Enemies hit too hard!" are such examples, i really only disagree with nerfing HP, some are likely to call me crazy on this.
Enemy damage probably would be reverted to Tier 3, but keeping their Tier 4 health in exchange.
Some of the best players reported so far having to use like 50+ Sparks of Life which is ridiculous, but i say in due time people will adapt having to go on the defense and that use count will drop massively and likely will become standard to us.
Although i hope to start seeing variety now with this, Shadow Lairs feel like a fresh new experience having to play like how some other MMO's tackle dungeon/raid content.

I do enjoy using stage-specific armour sets, and support bombing is my favorite way to play the game.
I can wholeheartedly agree that the damage enemies do has to be knocked down a level or two though for people who wear the proper sets. Not for people who don't adjust.

To answer your concerns about power creep though:
The powercreep wont take affect through stats climbing to insane heights. Instead, playstyles that are creative and teamwork and defensively oriented gameplay will be what gets stronger with time. At the moment, the only players who complain about shadow lairs are the ones who enter with no pre-meditation.
No formulated strategy. Just everyone trying to dps the hardest with full glass cannon.

When your full dps gets healed in a split second by a single silkwing, it's already too late to have realized that you needed venom veiler the whole time.
Gremlin menders giving you hassle and are too mobile? Torpor Tantrum shuts them up and opens them up to be killed. Well timed heart attacks on low hp enemies, super well placed pulsar shots, there are tons of possibilities for amazing teamwork with these new sls. It's not the gear that needs to get stronger, but just the way teams play together. I'm sure there's a perfect set of 16 weapons and great positioning that can make the sls a cakewalk, and these weapons might be weapons that were previously write-offs. When mixer doesn't 1 hit slimes, these crazy and amazing situations are opened up.

I'm glad to see unprepared parties being curb stomped because these lairs are finally making people think outside the box and strategize for once.
Taking the right armour should be more rewarding though. You can still get 2 or 3 shot even wearing the perfect armour that suites the lair.