Thresh has essentially always fallen by the wayside- being pushed out by folks running demolitionist or similar perks and especially neglected throughout super regeneration buffs being pushed into active generation and newer power creep perks. It even got removed from the dawning pulse, which was in a unique position of providing all ability energy and healing via presents while still having an explosion perk (headstone).

Now, in comparison to thresh's +1% super gains, we have:

• Dealer's choice which gives +0.3/1.6/3.0% gains for having more equipped
• Attrition Orbs generated 0.8/1.1% orbs just from hits which can be accelerated by multi-hit items like kinetic tremors
• Siphons are 2.5-4.4%
• Dynamo generates 2.5/4% for class ability near enemies
• Distribution is 2/3/4% for class ability near enemies
• Hands on/ashes to assets is undertested but looks to be 1-5% on the given ability kill
• Firepower/Heavy handed/reaper orbs are 0.8/1.1/1.25/1.5%
• Bad Juju giving +0.8/1.1/1.4/1.7/2% for each stack tier on top of reloads and massive explosions and the exotic damage boost
• Balidorse giving 2% per frost armor granted and up to 50% after super end
• Nighthawk giving 1.5-4.5% on any headshot kill and refunding 1/3 after a super kill
• Cuirass of the falling star giving 1.5-3% on amplified melee kill
• Doomfang ability punch kill giving 20% and refunding ult when active
• Unbreakable is the same but with unbroken blocked damage (20%)
• Geomags giving 2% per ionic trace
• Mantle of battle harmony giving 1.5-2.5% per enemy tier with matching weapon kills
• Raju's giving 1-4% per arc debuffed enemy kill and refunding up to 50% super
• Skull of dire ahamkara which hasn't been testing but likely scales between 1 and 4%
• Shards of galenor gives 2.5-5% on knife kill and refunds up to 50% after end
• Star eater scales gives 2% extra per orb pickup

I know exotics aren't comparible to legendary perks, but certainly similar perks that are found in the origin slot, or those that also provide armor charges are. The exotics give a good frame of reference that value kills around 2+% at the cost of the slot (and provide other much greater primary effects usually)

I didn't even bother going into team-wide energy generation with the big orbs (7% with benevolence, generosity, and similar), and the perks have to compete with not only consistency perks like reloads, but much higher ability generations (demolitionist at 10/11% grenade) which can clear ads and generate their respective mod super energy effects, or compete with explosive ad clear perks which already rival ad clear supers.

Ask yourself: "When would I use a thresh weapon?"

I don't think I have an answer for that, and I love super generation builds. I have 5 thresh weapons in my vault, yet not a single one is found in my many super generation builds- even though I've crafted a full set of dealer's choice gear for some of them. Even the crown of tempest one which should be PERFECT for thresh+jolting feedback has... a stats for all+jolting feedback pulse rifle instead because it's more consistent.