As a researcher, I managed to infect 10 monkeys using a alternate method but shortly after they evolved into Tier 1s, I quickly saw a few problem with xeno containment.
1. Xenos can kill unbursted monkeys in containment, denying some DEFCON -Is this xeno "RP" acceptable?-
2. Queen can banish other Xenos in containment, this does 2 things.
A. Denies Defcon to the marines (the corpses seem to "disintegrate" instead of leaving a defcon-providing corpse)
B. Awards larva "refunds" to the queen when the xeno dies.
3. The Xenos in containment can morph into an acid runner and suicide, thereby -again- denying DEFCON.
I would like to propose a few restrictions on xenos in containment.
1. The Queen can't banish Xenos in containment.
2. Runners cannot evolve into Acid runners in containment
3. Xenos cannot kill infected monkeys in containment? (optional, I'm a bit unsure about this)
4. Reduce Infection Burst timers in containment? (this could boost corrupted hive strategies)
5. Make infected things -no matter the degree of infection- count irreversibly towards DEFCON as if they were live xenos in containment. (THIS WILL NEED SOME WORK, powergame-prone)
-To be a bit spoiled-
Currently Xeno players have a few ways to powergame the containment mechanic using the above mechanics, (not that I'm above it myself) and it's just frustrating and LRP that they can do this ESPECIALLY the queen banishing xenos in containment, since it awards larva to the planetside hive, and it denies defcon to the marines. I like to think that my monkey-infection gimmicks can award DEFCON (and ideally alot of it), especially with how lucky research has to be to get an egg (or a vial) early enough in a round to infect monkeys in a time-relevant way, only for the rewards of your efforts and their circumstance to be thwarted like this.
-Admissions-
Firstly, my 3rd suggestion about Xenos being able to kill about-to-burst monkeys actually has some counterplay by the researcher; He can counter this by infecting all of the monkeys in short-order instead of doing it in batches (thus all of the monkeys will burst before they can evolve into Tier 1s.
My 4th suggestion is the most offensively selfish, but there is a bit of a gameplay rational to it; Typically bulk infections (or infections in general) happen so late in the game that any DEFCON rewards usually don't manifest (xenos took planet) or they happen in a HIGHLY untimely way (Marines are being forced to evac), so the rewards can't be captialized on most of the time even when infections can happen.
There is also some "gameplay" that can be enjoyed by marines (and to a lesser extent xenos) by having xenos in containment, since allows the LRP interactions between the two (and gives hyperthrottling more prominence).
This would also make the big game-changing tactic of making a corrupted hive a bit more viable as a game-ender; For most intents and purposes, a corrupted hive strategy will only manifest combat-capable Xenos by around 13:40-14:20 (I'm not exaggerating) and 8 times out of 10, the round would have concluded by some other means (nuke, Evac, Marine major, ETC) before then (a good IO has more game-ending power than a researcher). Admittedly (again) a corrupted hive victory is probably intended as a "super special" victory condition for the marines so it's probably implemented as such, being roughly a 2-5% chance per round even with a good researcher.
But ehh, even with all of this considered, I'm relatively OK with Xenos taking so long to grow, since it reinforces some interaction between command and research, I.E. research needs permission from command to begin infection since they'll be more in touch with groundside to see if it can be capitalized upon, (so they won't need to massacre monkeys if it fails). Or maybe you like Quasi-rogue Researchers who create this "Mess" for command to have to "clean up"?.
The fifth suggestion seems prone to powergaming, why not drag infected marines to containment to "cash in" the reward they have in them, and then head them back to medbay to remove the alien? What's to stop the marines (or researcher) from infecting a monkey and then ODing them on Quick-clot to cash in on the DEFCON? Naturally this suggestion can't be implemented as-is since it's the most prone to exploitation, but there is something useful it in, since it effectively will allow you to ignore all other suggestions I made while still giving what I want -Not losing DEFCON from dying Xenos in containment-. The implementation has another problem; It's unintuitive, -like the rest of the game-. How would a researcher know that this "cashing in" feature is in the game so that they shouldn't feel too upset that the precious living Xenos are killing each other and assume they're breaking LRP and doing straight powergaming?
A suggestion to make it clearer is to upgrade the containment consoles so they "take pictures" or "collect motion data" or something about the xenos, that incurs a one-time DEFCON reward from the xeno or something (this will still screw gameplay involving Xenos in containment).
The first and second suggestions kinda are wishy-washy about the implementation now that I think about it. If the queen is smart enough to hijack a dropship (absurdly even, as if she's a super-hacker) then she'd be smart enough to realize something is fishy about the "tallhosts" growing xenos in containment, and since it's relatively accepted that the hivemind is a "super-radio" that allows communications to orbiting xenos, she'd know about it, and order the killing of her "children" -that makes sense-. (maybe add in a "They're too precious" UI prompt to a queen that tries to banish?)
But It's also plausible that the Super-radio the xenos get might be muffled or unclear to xenos in containment due to "static" or something so a banishment order won't get through to the contained xeno, giving a vague RP reason as to why they can't just kill contained xeno.
-closing thoughts-
The only way the marines can KINDA counter these tactics would be pretty unfun for the Xenos; The humans essentially torture/suppress the xenos (as soon as a drone drops weeds) with gunfire leaving them in pain-crit the whole time. But just because such tactics MIGHT be plausible, doesn't mean they should be used to restore effectively what is plainly assumed (having xenos in containment plainly).
I suspect that it's still possible for a xeno to commit suicide through some hidden "kill self" button somewhere in the code, I've seen a solitary dead runner in containment before acid runners were a thing.
I still think you should buff the gameplay of CTs.