How to Make a Party With No Weaknesses Panic

I've briefly spoken before about the party of 7 that I am DMing a campaign for. The difficulty with a party of seven in terms of game mechanics can come down to one word: coverage.
There are simply no weak points. They have great front-line in the paladin, druid, bard and ranger, there is excellent magic support with the wizard, the druid and the bard, the ranger, rogue and fighter make great ranged support. There's almost no way to hurt them or make them start panicking. If a character goes down, there are enough party members to stabilise and heal without any major tactical changes happening. So I came up with the perfect solution.

The party was in an abandoned archive when a group of constructed warriors entered and opened fire on the group with javelins. I was using the standard warforged soldier statblock from the Wayfarer's Guide but with one minor change: they had a massive green lens for a face. This was a scry lens, used by the mysterious creator to watch the party fight. They dispatched the automatons with some ease and didn't give it a second thought. Which is where my next trick came in - the upgrades!

The upgrades were deliberate. An extra attack, minorly improved health and AC but it was the secondary abilities that did the magic: firing a net and firing poison darts. Here is my reasoning for why the inventor made these changes:

-the paladin is pretty much unhurtable in combat: AC through the roof, a health pool that a demigod would be jealous of, and smites out the wazoo. Don't target paladins in combat, make them rely on saving throws.
-the ranger and rogue are hard to hit once off, but when you surround them after poisoning them, it makes it much easier to hurt them.
-bring the fairy archer out of the sky with a net and nullify all those advantages she brings
-the wizard must be able to move to cast spells so net him so he's without a somatic component
-the druid needs to have their priorities split and also be hit enough to come out of wild shape.

But there was also a tactical change to their approach. It was an ambush in a narrow street.

And it went so well. The party couldn't keep a formation that kept the wizard safe so the wizard went down, the rogue went down, the paladin was useless under a net and couldn't protect his charge (the druid), the fairy escaped the net but had so many targets that her attacks felt pointless. Within 4 rounds of combat, I had brought a party that felt no fear or worry to the point of panic.

Not that I play with a mindset of DM vs players: it was actually an exercise for me to see just how strong this group of level 7 adventurers are so I have a baseline of where to aim my encounters going forward. That and also it's what my BBEG and his lieutenant (the inventor) would do: upgrade to counter this group and put them down, make sure they aren't a threat anymore.

The next upgrades? Well, I'm still not sure. I'm thinking an anti-magic poison on the blades that on a critical hit burns away a spell slot. Plus smoke grenades to separate the party even more. But I have yet to decide.

Until the next time folks

Yours faithfully hiding inside the statue of Lathander
tomster-17