Here is your solution, like it or hate them, it fixed us from barely killing haat to doing 2x hstr per week.
1. Find a guild in your same boat, propose an alliance, NOT a merge.
2. With said guild, establish your best 5-10 from each that communicate openly and are readily available when you need them. HSTR ready.
3. Coordinate dates to do hstr. We use discord.
We currently WILL do hstr during a merged TW and remerge after the TW. We will NOT sack a TB. I suggest this as there is really no other way to pull off 2x hstr per week.
4. Create a channel dedicated ingame to hstr or whatever you are doing that all guild members can see. This channel is solely for the purpose of providing information for said events. Utilize your TOPIC to broadcast the dates and notices. Communication is key here, and whoever is leading needs to promote this. The lazier players need to find the info, not just your small core.
5. Implement the rule guild event participation is required or it's a kick. Now I've gotten a LOT of heat over this, but it is ultimately going to be what sets your guild tone.
6. The evil necessity. Win, at EVERYTHING. Phase 1 TB? WHO MISSED THE SPECIAL MISSION? Rancor sim? WHO DIDNT JOIN EASY WINS? WHO DIDNT JOIN TW? ... find them and warn them or kick them. I have members who used to absolutely suck, and stepped it up big because someone was willing to work with them.
Follow that and you can get hstr done. We did, so I know it works.