Spoiler:The B on Runners stands for Base Runners, I'm not going to acknowledge Acid Runners in this due to them being less relevant to this and the fact I barely play them and can barely make a judgement of their balance.
Introduction:
Spoiler:A look at a different thread inspired me to make, as this goes beyond the scope of that thread.
I know many players think Runners or Marines are overpowered or underpowered or unfair in their own ways. I'll be going over this with a slightly more mechanical/code favored lens at where Runners and Marines have stood since Maturity Removal(I will not be covering anything during maturity as I know almost nothing firsthhand and very little secondhand knowledge on Runners during this time.)
I will be separating this into general time periods that will not be given actual dates.
The Forgotten Age:
Spoiler:This was time period when Maturity removal had just happened and a few months afterwards. I can't say much about it besides some generalizations. However during most of this Runners were more powerful than their modern counterparts thanks to evasion(for those who don't know many xenomorphs had a chance for bullets/projectiles to miss regardless of a weapon's accuracy) and tackles being quite powerful. Runners barely solo-capped during this time, just because solo-capping was a Sentinel designated task. Basically runners could solo-cap better than they can today, but they just didn't. Runners that did capture marines normally happened when a Queen screeched.
The Unfair Age:
Spoiler:This time period started when a Coder had made a PR that heavily changed ALL xenomorph disarms/tackles to require between 2-4 disarms at minimum and a maximum of 4-8. There was between a 15%-40% of a tackle landing before the maximum. This all depended on xenomorph caste. I believe sentinels also received a nerf to their neuro during this time. However Runners own disarm/tackle was 2-6, with a 25%. During this time solo-capping had started becoming more frequent from Runners. Not because they were good at it, but because I wanted Runners to Solo-cap and personally led them onto this path during this time.
In terms of balance it was horrible for both sides. Runners could not by themselves keep a marine indefinitely stunned by disarming at max speed, via rng a marine WOULD get up eventually making dragging marines away from Queen screeches a bad idea without an egg morpher, eggs, or hugger traps nearby.
However, because of the wildly varying rng, Runners could also solo capture a marine like Ethan Weiss with no ability for them to fight back. A runner could pounce a marine, disarm twice, and get a tackle. Then immediately start devouring and have a roughly 60% to devour and keep the marine pinned with more successful tackles. However the other 40%ish time the marine would stand up and run/kill the runner.
Due to no respawn timers on pooled larva and this method mathematically favoring the Xenomorphs, Runners intending on capturing marines would throw themselves at lone marines with little regard for their own life. If the runner failed and died, they would just be back within 2 minutes and repeat the process until RNG sided with them.
This time period lasted about 3-4 months.
The Golden/Runner Age:
Spoiler:The start of this age was brought about by a PR that changed Runner tackles to be between 3-4 tackles with a 40%, as well as altering the values for other xenomorphs. As many know, this was entirely unbalanced and favored to the xenomorphs. As disarms weren't reset by pouncing, any lone marine would probably become a free capture for a competent runner. This is also when I changed my own name to TKO.
During this time marines would commonly go off alone to perform some minor task/to cover more ground or just be a carefree IO. Such behavior often resulted in well over 10 marines being captured. Some xenomorphs ended up deifying TKO during this time(thankfully that's over it was kinda cringe)
Overall, towards the end of this age, xenomorphs became quite powerful overall, due to xenomorphs fully utilizing their powers. Such as Warden Praes healing themselves in the middle of combat. And the win/rate reflected this change. Xenomorphs won hard because a decent number of players became very skilled at using very powerful castes, very well.
This age also saw the removal of armor degradation.
The Downfall:
Spoiler:This age featured heavy nerfs to many xenomorphs and some balance changes still kept today as well as the introduction of techwebs at the end of this period. However this time period was started by the marine players themselves, not the coders or staff. Specifically the meta-changes of marines always traveling in groups, sticking to a buddy, and starting small-large size runner/lurker/predator killing teams. As well as engineers taking cading VERY seriously and making far more robust defenses and guarding/manning these defenses. This popularized behaviors, such as highly competent marines patrolling heavily walked routes to prevent lone marines from being killed or captured(like Hydro road on LV); one or two highly competent marines leading as a defacto leader of less competent marines to scour and remove tunnels/lone xenomorphs skirmishing marines.
These meta-changes were largely driven in response to runner mains from the Runner Age. Although this period also saw Coders implementing code solutions to the Power imbalance they saw in the Runner age. This resulted in a heavy cascade of changes and nerfs that effectively nerfed xenomorphs overall into the ground.
These are : The removal of Evasion from almost every xenomorph. Hp, damage, and ability usage nerfs for most T2s, T3s, and the Queen. Nerfs to Sentinel neuro spit. Runners tackle % reduced, and pounces resetting disarms. Warden armor and self-healing removal. Various armor balance changes(mostly nerfs). Survivors receiving 20% knockdown resistance, heavy neuro resistance, and a 75% bonebreak resistance. Delimb and bonebreak chance being heavily decreased(and refactored).
This time also saw admins and coders publicly and secretly testmerging Runner disarm and tackle nerfs. This was mostly secret testing and left runners unable to keep humans indefinitely tackled. At one point they kept one of these secret testmerges in for about 3 weeks. This time period also saw some changes to medical and bodily damage such as heat damage being removed from corpses. While these made quality of life improvements to marine gameplay, it also made marines more powerful.
Modern:
Spoiler:Where we are now. Techwebs are bit more balanced, base runners have been nerfed a bit, but differently from the testmerges and deservingly so. T2s and T3s have had HP improvements, reverts, and rebalancing. SMGs are in a better spot, and the game is more "balanced" in some people's definition. Though it's the present so you have your own opinion on how it's going.
Afterthoughts:
Spoiler:I tried to be somewhat unbiased in this, and tried to be accurate, though memory fades with time so I'm probably better off writing this now than waiting longer. If I got something wrong it's because I'm trying to remember it off the top of my head.