we had that already some time ago:

it was a pain with a sequer full of looted missile launchers or armor plates moving with average 2 kph

remember, the cargo system is based on volume, not mass. also your robots cargo is a compressed teleport buffer (cargo is stored in form of energy - or how would you explain that a sequer could transport several heavy mechs and tons of ore)

You are forgetting to consider other factors in mechanical design, such as engineering for loads.  Given a sequer's visual design and stated purpose, I would expect its rated (equipment screen) performance to apply for a full cargo load, not an empty hull.  Its optimized to be a hauler, not a combat bot.  If anything, I would expect it to be *faster* than rated for an empty hull, though this would be a limited due to the tradeoffs involved in engineering and gearing a torque-heavy drivetrain to support the 80U cargo load.

If cargo stores in a form of an energy: why my reactor or acc. recharge time still same? Maybe mass in cargohold transmutating in pure volume of green butterfly energy or something else. I can write here 100500 such histories about teleporters and mad squirrels in gophos head.

The main point of this topic is bring cargo into a game mechanics.
For example: CPU run navigation program in parallel thread. Installed modules reduces speed because of CPU load. Total robot weight reduces speed too, but less than high CPU load.
/*A really big set of formulas, what proofs my idea*/

Any other thoughts?

Yes, i'm agree. This is a lot of calculation, but we dont know certain how implementing of this system will affect server performance, because server-side written by DEVs not us . So time will show. I really want to see less such weird thing in this game.

Ignoring physics one one hand then suggesting fixes to mechanics that require it on the other hand makes my head want to explode.

Either the cargo is materially in the hold, which means you'd need a bot larger than a Mech to carry a mech, or its not materially in the hold. Since a sequar can carry a mech, it can't be materially in the hold. Therfor the arguement about mass vs speed is moot.

From a game play standpoint, moving slower with cargo is not fun. I don't care how much memory it takes on the game server, or how the game database can be setup to allow for it. 90% of the transport people will just stop playing, the other 10% may continue to haul at 15kph, but the game will grind to a halt from lack of material.

And the transparent troll by OP to try to slow sequars down to make them easier to kill is transparent.