Right now, this game apparently processes data at a similar rate to an FPS.

Spiral Knights is more like a first person shooter in terms of the way we perform networking. - Andrjez

But I am able to play it entirely one-handed if need be, regardless of how difficult the game actually is.
Using my mouse, I can set block, strafe, attack, move and change weapon. All in one hand.
And play to a level similar to those using a controller, if not better.

What I want to know is fairly simple. If you're anticipating a level of activity similar to an FPS, but I can play the game one handed, what are you going to do to change how intense the game is?
It shouldn't be possible to play an Action Game one handed. Ever.
I have a few solutions, though.

More intensive attacks

Give certain weapons special attacks, ones they can perform during a combo or after a charge attack if they time it right.
If a player suddenly changes direction on the 2nd or 3rd hit of a combo, it might do a high knockback overhead arc, like the Troika's charge.
This would allow you to hit monsters away from you if they got too close with weapons of all speeds.
It would leave you vulnerable afterwards, however.

Some weapons with long charge attacks, like the Troika, could have a cancel, that still deals a fair bit of damage, but not full damage or knockback.
If you attacked right at the peak of the attack animation you could damage an enemy twice, but leave yourself more vulnerable afterwards.

If you're moving in a certain direction during an attack, you might be able to do a different attack.
Bombs could be thrown in front of you if you move backwards while dropping it.

Guns wouldn't get any special attacks, instead you would be able to switch to them almost instantly during a sword combo.
Guns could become special attacks, allowing you to chain combo your gun and sword.
Hit once with your Khorovod then when you hit next or previous weapon, pull out your gun and do an attack.
Faster weapons would switch and attack quicker, allowing for this to create some damaging combos.

Cap charge speed

It's kind of ridiculous how fast some weapons charge with a few Ultras on hand.
It needs to be capped at a certain speed, because it is so easy to rely only on the charge attack of a specific weapon if you move fast enough.
Especially with guns.
It needs to be lowered overall so that all weapons can do one fairly easily, but not able to be reduced so much I can accidentally shoot a charge attack off when I'm normal firing (which has happened before).

Change bomb function

Bombs right now, are all charge only. Which, while it balances out bombs, it makes them difficult to use and generally, less fun to use.
If they're too powerful to be used as a main weapon, turn them into sub-weapons.
Being a sub-weapon, they are usable at any time. Like flasks, you would hit the bomb button and the bomb would come out. You could then cook them or drop them. You would use switch weapon to put the bomb away if you decide not to use it.
You would only be able to carry one bomb at a time in the sub-weapon slot, to balance this out.

Bombs would be able to dropped in groups of 1, 3 or 5, depending on the type.
Two bombs could not be dropped within the same explosion radius, as to stop monsters being damaged more than once by the explosions.
Crystal bombs and Gravity bombs would only be dropped one at a time, but have increased range and slightly higher attack.
Blast bombs, Vaporizers and other similar bombs, would be able to be dropped three at a time.
Five at a time bombs would be Proximity Mines.
These would be bombs that could be dropped, but only explode if a monster enters the radius.
The radius would be so small and their damage would be pretty average, that it would take one and a half mines to do the same damage as one bomb.
They're for blockading routes, slowing down or snaring enemies that chase you, as well as just an alternative to regular bombs.

Now here's the big change.
Bomb placement could be out all at once, but they would have a recharge time that starts from their explosion time.
So, if you drop three bombs at once, it might take you thirty seconds to drop them all again.
Dropping Five Proximity mines would mean having to wait until they explode or expire (without an explosion) before they count down.
Cooking (charging) a bomb, would decrease the recharge time of bombs, but also reduce the number you would be able to drop at a time.
You wouldn't be able to drop three charged bombs all at once, but dropping three charged bombs would stop you dropping bombs for a shorter period than dropping them all at once.

Changes to energy slots

This one is pretty simple, but they should come in 7 log-in day forms, for those who play more casually. For 50~75 energy a piece so free players would have access to them.
The 30 calendar day forms would be 150~200 still, to make it more affordable than buying 4 log-in day ones a month.
It would allow free players to use them without forcing them to buy CE on the exchange and allow more casual players to spend less energy.