A simple suggestion that seemed direct enough to justify its own thread.
TLDR: Energy Siphon should replace Energy Drain when it is learned at the appropriate level. Energy Siphon should do the same single-target damage as Energy Drain with bonus AoE falloff damage.
This is a change that would already be welcome in 5.x, and it makes even more sense with Endwalker's fully-revamped Summoner. That said, it can certainly wait for a post-release patch alongside other job adjustments.
Long-winded reasoning: generally, having separate single-target and AoE abilities works well; they add flavor to each job and provide opportunities for enjoyable optimization. I'm thrilled that 6.0 SMN will have dedicated single-target and AoE Actions for each Demi-Summon and Gem-Summon. Meanwhile, Summoner's flashiest abilities like Akh Morn/Revelation, Summon Ifrit/Garuda/Titan, and Deathflare will all be single-target heavy-hitters with AoE falloff damage. This makes perfect sense for the identity and functionality of the job, and I can't wait to try it out!
With that in mind, this brings us to Energy Drain and Energy Siphon. They are not flashy, high-powered abilities. However, they also aren't key to the identity of Summoner in FFXIV or the rest of the series. As it stands, these abilities perform nearly the same functionality, they share the same somewhat long cooldown (twice as long in Endwalker!), and Energy Siphon will always be used if more than one enemy is present...so do we really need both Actions?
In the interest of reducing button bloat (especially important for controller users), making the job flow as tightly as possible, and introducing room for new Actions in future expansions, please consider "upgrading" Energy Drain into Energy Siphon at the appropriate level via a Job Trait.
Ideally, the new version of Energy Siphon would do the same single-target damage as Energy Drain, but retain 5.x's AoE utility via falloff damage. It should be noted that I'm not suggesting specific potencies or percentages for falloff damage — I realize that 200 potency damage with 50% AoE falloff does more damage than Energy Siphon's current implementation, which raises concerns regarding job balance.
Upon implementation, Summoners will only need Energy Siphon to get their two Aetherflow stacks every 60 seconds. The additional hotbar space could then be used for future Actions or even something like maintaining Ruin II's current functionality as an instant-cast spell that is separate from Ruin I/Ruin III.
(I'll also note that I have no qualms about the changes to Ruin II for Endwalker, but I imagine that there are some Summoners that are sad to see it go. Naturally, if it was brought back, its hotbar button would change to Ruin IV whenever Further Ruin is active).