Oberon is an extremely versatile support frame that's mostly irrelevant past midgame: despite having a well-made kit with great synergy between his skills, he is very difficult to build (requiring way too much of too many stats to be played comfortably) and struggles significantly with Energy economy when not playing solo. This post is meant to propose buffs to his existing kit, while not making other Warframes seem weak in comparison. Additionally, all these skills make use of mechanics that already exist in-game, as an attempt to minimize the need for additional programming should they be implemented.
Passive - All of Oberon's skills have +100% effectiveness against Companions.
The 25% bonus to Armor, Health and Shields is not especially useful when pets as a whole are known for their frailty, especially when these values only stack additively to the existing Link mods. This new passive would keep to the theme of buffing companions, while being more useful overall.
Smite - Keep as is, or buff bonus damage to 50%. Increase Radiation status effect chance on the orbs to 100%.
By itself, Smite isn't a great skill, but it has a fantastic augment and scaling damage (horrible scaling damage, but damage nonetheless).
Hallowed Ground - Buff the base radius to 250° (enough for Stretch to be enough to cap it at 360°) and consider increasing the base Duration to 30 seconds and the base value for Iron Renewal to 300.
Hallowed Ground is a great skill: it deals respectable damage and provides constant soft crowd control so long as it's active. However, it requires way too much modding to be at maximum effectiveness. Very slight stat tweaks would make it much more convenient to use.
Renewal - Cap the energy drain at 10-15/second, make the augment built-in and consider either buffing the base value to 50/second or making it percentage-based, like Garuda's Blood Altar.
Despite having a higher base value when it comes to health/sec, it's inferior to Wisp's Health Mote in essentially every way. Oberon is punished for being in a group by having an Energy Drain that's hard to sustain, especially when considering the need for high Strength, Duration and Range for the rest of his kit makes it difficult to cap Efficiency. Assuming a 4-person squad with Companions, Oberon would have a base drain of 15 energy per second: should one of these squadmates be a Nekros with Shadows of the Dead active, that value is further increased to 22 energy/second. Making the augment built-in would additionally free up a mod slot for his build, thereby increasing player choice.
Reckoning - Make the base armor strip 65%, remove the need for comboing with Hallowed Ground in order for armor to be stripped and change the health orb drop chance to work like Blazing Chakram. Additionally, fix it working in the Steel Path.
Reckoning is both a nuke skill that can't nuke, and an armor strip skill that can't strip armor. The base armor removal value (35%) is low, especially when compared to other frames (most notably, Caliban), and it only applying to enemies standing on Hallowed Ground makes it too expensive and unreliable for regular use. The reasoning for increasing the armor removal value to 65% is to make it comparable to Caliban: while his Fusion Strike is only 50% at base, it creates a zone that strips the armor of any enemies that walk into it, as opposed to Oberon's need to recast it for each new group of enemies. Additionally, 65% is just enough that +55% Power Strength (equal to two Umbral mods or Transient Fortitude) would be enough to cap it. Making the health orb drop chance function based on enemies being hit as opposed to being killed by the skill would help it remain relevant past the point where enemies stop being one-shot by it, as well as increasing build variety by making Health Conversion a viable option. Lastly, the armor strip on Reckoning has not worked with enemies that have bonus armor (like those in Sorties and the Steel Path) for over three years at this point. Fixing it would undoubtedly increase the amount of people playing him.