The key element of swarming is that you can do it knowingly, or accidentally; presently the AI does it a lot of swarming accidentally, a big factor behind its endless stalemates against itself. Another key element of swarming tactics is to mentally separate units into expendable and in-expendable units (heroes are the latter), in the earlier waves of the swarm and plan your retreat so that low-level units are sacrificed to ensure the successful retreat of high-level units.
You do realize that in all 4 images your armies are a random assortment of units with 0 synergies, random tiers and no singular focus.
Those armies are literally what an AI would build, just lower in tier. You wouldn't need to send 3 waves if you made stronger armies.
I've had no trouble beating a "Brutal" game mode (so not just the AI itself) with 3 strong armies and some teleporters to move around.
I would usually aim to build up 6 armies so that I could send 3 to go murder someone and keep 3 near home to clear incoming threats.
First of all, pick a class. Pick Ranged/Battle Mage/Shock or Skirmisher as your "damage dealers". They will be your primary focus.
In the case of Shock and Skirmisher you quite literally want to mono stack them. Shield/Polearm/Support will not help them.
The only exception being if you're able to get these units mounted or are using Athletics so they can keep up for the most part.
Why? Because map movement dictates how fast you can farm for resources/XP and how fast you can reposition your armies.
Now. If you chose Ranged or Battle Mage, there is a benefit to combining them with Shield/Poleam/Support units as well.
Not random low tier trash. Units of either the same tier or one tier lower at most. Bring 1 per army maximum, no more.
You have your Shield and Support units purely for their auras and additional effects (if available), that's their only role.
Polearms are used as a frontline replacement for Shield units or to counter a potential Shock based composition.
The more enchantments you can stack for your chosen "damage dealer", the stronger you become. That's how the game works.
I'll give you 3 example builds that revolve around a specific core unit and aim to empower it as much as you possibly can.
You also always aim to pick Form/Society Traits, a Ruler and Tomes that cover your weaknesses while empowering your units.
For this build you focus everything on your mounted unit roster. Archer is a no-go, everything else can be played with.
You pick up purely melee based enchantments, focusing as much as possible on buffing your (Aspirant) Knights.
There is Staves of Grace if you bring some Champion/Legend rank Bannermen, as they are still decent late game.
Liege Guard also benefits from the chosen build, you generally want 1 per Hero, and they're mounted. So this is good.
In this build you are focused entirely around Spell Shield/Soother/Spellbreaker until you unlock Geomancers.
Everything you unlock focuses on buffing Battle Mage/Support and Shield units. Forget Iron Golem, it's shit.
You stick to your 40 movement racial units and try to keep Spellshields alive. Otherwise go full mono Geomancer.
If you want more frontline, you can use your Ruler and Heroes to fill the gap. A Ritualist replaces your Support.
You do not drag around T2 units unless they are Champion/Legend. And you don't bring garbage non-racials.
It would be great if Rock Giants and Golden Golems were good as a late game frontline, but they are sadly bad.
This one is a bit more out of the box. It's a super strict build that stretches affinities for maximum gains.
You are giga focused on research, unlocking Stormbringers as soon as you can possibly manage.
Enchantments/Transformations focus on helping your Stormbringers with only Tome of Faith as outlier.
Your early game consists purely of Protectors and Animists until you're able to summon Mistlings.
These units and your Heroes do the early lifting (with some enchantment support) until Stormborne.
You pretty much just stack as many Mistlings as you can to farm the map with 40 movement units.
And then you mix in Stormbringers, which also have 40 movement, for the final army composition.
If you are playing in a different way, it's not wrong. But it is undeniably suboptimal. Therefore it feels bad to play by comparison.
The moment something is suboptimal and doesn't feel good people will generally avoid playing it, this is just human nature.
Swarming tactics will never work against a human player and wouldn't work if the AI was even a little bit competent at playing.