So you get to spend more money for tech labs that get to go into battle. So instead of having them safely tucked away in my back planets behind star bases and behind my fleet, I now have the privilege to take them with me in front of his fleet as well.
That's the fundamental problem in your thinking: Normal Labs and Shipboard labs are not mutually exclusive- the point of shipboard labs is to upon research to instantly gain a few extrra labs fro mthe capitalships you've already built, as well as to make new capitalships more appealing investments.
The purpose is not for conventional labs to instantly become obsolete- regular labs should be better at being labs, but the capitalships also contribute to your military and grant income with another vasari loyalist tech.
Also, killing labs is easier then killing a well microed capitalship- the lab can't run away, and aside from the advent has no shield mitigation. Not to mention, without capitalships you often need more labs then you can fit on 1-2 back-line planets.
If you want to take logistic slots into account when assessing the cost of tech labs then lets be fair and take into account the flat 9% tax from fleet supply along with the cost for upgrading for more capital crew. So yeah, I guess instead of paying the nominal amount of resources for logistical slots I get to have a amazing flat tax on all my income instead.
That cost is for your military power, not for the labs. This is your problem, you're attributing every cost of capitalships direct and entirely to the shipboard labs. Shipboard labs are supposed to be a side benefit of having capitalships, not the other way around.
And frankly, being to invest all those extra logistics in trade ports can easily more then make up for a bit of extra fleet supply-
Just because the tech labs are mobile doesn't make them better. Now instead of having to bypass my fleet and try and take out my tech labs while keeping my fleet occupied with a smaller force, my opponent has the pleasure of being able to bring his full force to bear on them.
Frankly if you take heavy capitalship losses, the opponent has a alrge military advantage and you're probably losing anyway.
Also you're again assuming you don't have any static labs. Think of it this way: you and opponent A each have 3 capitalships and 6 reserach labs of various type. Suppose you research shipboard labs and it only gives 1 lab of each type:
You are now 6 labs up on the opponent for just north of 1000 credits for which he could buy maybe 3-4 frigates. Even if your capitalships get killed, it's not like you suddenly are lower then him: no, you still have the same 6 labs as him.
And frankly with how powerful those cheap extra labs are, there should be a risk. At present there isn't much of one, because actually causing the vasari Loyalists to lose access to important techs requires a near total wipe of his capitalships as it doesn't take very many to have 8 labs of each type.
Ship board labs are in a precarious position as is. If they get nerfed any more there is literally no reason to take that tech aside from having the immense joy of watching your tech *and* fleet get destroyed.
Bull. Tell me a single TEC or Advent with as much impact on the game at a comparable tier to Shipboard labs. A mere 200 credits and change instantly grants access to easily 4000-6000 credits and 16-24 logistics worth of labs. Vasari Loyalists are the only race in the game that can reliably get to 8 lans of each type in multiplayer- that is a colossal tactical advantage. Every other faction needs to choose between a strong economy and a strong military: the Vasari get to have both for less resources then other factions get one.