I'm tired of trying to find the history of balance changes so I'm going to leave this here. Maybe it will get elaborated on, hopefully I will update it when new patches are released.
At this stage it only includes patches which were marked by a forum thread so some may have been missed. The descriptions touch on what seem to be the most important points (some in hindsight).
This page on Github has a (mostly?) full list of balance changes by patch but is long.
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1.6.1.6 - 13 January 2018 - Lobster added, Siren reload time increased, Racketeer nerf, Archer water-tank mechanic removed, All slow waves damage enemies only (Limpet, Com slowbomb, DRP), Gunship cliff behaviour improved
1.5.10.2 - 22 October 2017 - Unit renames and minor tweaks
1.5.9.3 - 24 September 2017 - Claymore tweaks
1.5.8.2 - 17 August 2017 - Athena made a strider, Faraday weight increase
1.5.7.8 - 26 July 2017 - Flail nerfed, Angler buffed, Hacksaw changed
1.5.7.1 - 2 July 2017 - Defender cost decreased a bit, Limpet added, Overslow added, Claymore rework, Siren range reduced, Shiparty nerfed, Reef disarm missile,
1.5.6.0 - 2 June 2017 - Defender cost increased a lot
1.5.5.0 - 21 May 2017 - Firewalker and Penetrator speed reduced
1.5.4.11 - 13 April 2017 - Disarm fixes
1.5.4.4 - 9 April 2017 - Buffs to Banisher, Copperhead, Hacksaw, Jack, Mace, Roach, *Rogue*, Skuttle, Sumo, Tick, nerf to Dagger, Scalpel, Flail, Glaive
1.5.3.4 - 8 March 2017 - Glaive and Rocko buffed
1.5.3.2 - 5 March 2017 - Commander HP increased, Slasher AI improved, Racketeer cost increased
1.5.2.24 - 20 February 2017 - Wyvern reload time increased, Hawk buffed, Rapier and Flail nerfed
1.5.2.20 - 14 February 2017 - Defender reload time increased
1.5.2.5 - 1 February 2017 - Tremor buffed
1.5.1.5 - 13 January 2017 - Initial storage moved to commander, Goliath slowbeam buff
1.4.12.15 - 22 December 2016 - Siren nerfed, Shiparty projectile speed increased, Mistral missiles replaced with rockets, Dominatrix buff
1.4.12.9 - 9 December 2016 - Siren cost increased and flex-AA capability nerfed, Duck torpedo range increased, Corsair reload time decreased
1.4.12.7 - 8 December 2016 - Sea/Ship rework, Sonar roughly equal to LoS, Serpent removed, Siren added
1.4.11.0 - 1 November 2016 - Raven dives only as far as necessary, Commander Lightning Gun nerfed, changes to burst laser and rocket firing AI, Reef no longer has antinuke, Advanced Radar no longer decreases wobble
1.4.9.2 - 18 September 2016 - Bantha and Detriment larger hitvolume, overkill prevention for artillery/rockets against structures (with next patch) and for Placeholder
1.4.7.0 - 7 July 2016 - Racketeer nerfed, Commander Plasma Artillery removed
1.4.6.0 - 1 Jun 2016 - Wasp becomes Gunship constructor, Freaker -> Constable, Target behaviour changes. (Also from 1.4.5.0: Swifts pull up from strafing runs.)
1.4.4.0 - 25 Apr 2016 - Raven dive-speed buff, user interface buffs
1.4.3.3 - 12 Mar 2016 - Warrior nerf, Valkyrie nerf
1.4.2.13 - 28 Feb 2016 - Commander weapons tweaked, Warrior partially nerfed back, Hammer and Pillager accuracy improved
1.4.2.8 - 13 Feb 2016 - Warrior, Angler and Hacksaw buffed, Lightning guns made more accurate (affects Zeus, Commander, Scorpion and Bantha)
1.4.2.5 - 2 Feb 2016 - Dynamic Commanders, nerf to drones
1.3.12.1 - 20 Dec 2015 - Small Rocko and Spectre (Sniper) buff, Dagger and Mace buff and Scalpel nerf, Duck range decrease and sonar increase, Pyro death sets fire to ground, Recluse range buff, Unit AI improvement
1.3.11.1 - 11 Nov 2015 - Skydust nerf, effectively increased minimum range
1.3.11.0 - 09 Nov 2015 - Doomsday Machine hit with the nerfbat
1.3.10.0 - 31 Oct 2015 - Blastwing fireball explosion, Line of Sight changes
1.3.9.0 - 19 Sep 2015 - Removed personal jammers, units cannot jump out of water, Dominatrix targeting improved
1.3.8.12 - 19 Aug 2015 - Kodachi LoS increased, Panther HP increased, Vulture jams
1.3.8.9 - 15 Aug 2015 - Starlight targeting and Transport behaviour fixed perfectly and forever, Valkyrie accel/deceleration buffed
1.3.8.7 - 13 Aug 2015 - Circleguard implemented, Zenith gathers asteroids
1.3.8.5 - 11 Aug 2015 - Panther and Dagger range increased, Pillager and Zeus more accurate
1.3.7.4 - 29 Jul 2015 - Constructor and commander metal shared
1.3.6.8 - 28 Jun 2015 - Wyvern missile no longer homes, but predicts movement better
1.3.6.6 - 23 Jun 2015 - Wyvern missile homes
1.3.6.5 - 21 Jun 2015 - Scallop underwater damage and reload reduced (overall less DPS), Blastwing has better accel/deceleration
1.3.6.1 - 16 Jun 2015 - Units may now jump onto buildings, Antinuke behaviour improved
1.3.6.0 - 11 Jun 2015 - Jumpfac units buffed, Ship units generally buffed, Sniper nerfed, Recluse buffed, Firewalker shotgun, Scallop shorter range
1.3.4.1 - 3 Apr 2015 - Raven speed nerf, Slasher overkill prevention
1.3.1.17 - 28 Jan 2015 - Nano-shielding removed, Vandal overkill prevention
1.3.1.13 - 24 Jan 2015 - Weaver buff, Rocko health nerf
1.3.1.8 - 17 Jan 2015 - Overpowered Missile Update
1.3.1.5 - 11 Jan 2015 - Damage fixes and small health tweaks
1.3.1.0 - 6 Jan 2015 - Banisher lighter and rerole, Sumo buffed, Funnelweb nerfed, Gauss regen, Wolverine nerf
1.2.12.0 - 30 Nov 2014 - Reef remodel, Mace nerf, Dagger range nerf, Sonar heavier
1.2.11.0 - 31 Oct 2014 - MORPH REMOVED, Bomber rearm before repair
1.2.8.18 - 30 Sep 2014 - Superweapon changes
1.2.7.11 - 8 Aug 2014 - Duck range halved, Claymore heavier, Ship tweaks, Kamikaze wreckage
1.2.7.9 - 3 Aug 2014 - Dagger cost increase, Mace speed nerfed, Lveh nerfs partially reverted, Wolverine fires backwards
1.2.7.0 - 30 Jun 2014 - Bandit cost reduced, Outlaw speed increased, Dirtbag armed (IIRC its attack was quickly reduced), Pyro HP reduced, Jack cost reduced slightly, Rapier slow, Brawler range buff, Trident rework, Rocko nerf, Sonar range drastically reduced, Ships reworked.
1.2.6.0 - 1 Jun 2014 - Rocko speed reduced, Gauss pierces water, Commander Gauss removed, Duck buffed, Urchin nerfed
1.2.4.9 - 23 Apr 2014 - E-Cell removed, Wolverine mines cloak fixed, unit renames
1.2.4.0 - 7 Apr 2014 - Sea balance; Claymore added
Stopping here is largely an arbitrary choice based on it being entirely before my time, and changes beyond this point probably aren't super-relevant today.