The main reason why people complain that thermia fracture sealing is too long and boring is because there is currently no way for players who are skilled/ better geared/ better coordinated/ better informed to speed progress up.
This was a problem that I thought the devs had solved going from POE to Orb Vallis bounties. Some of the longer POE bounty stages involve standing there waiting for a timer to run down like for the mobile defense or capture the camp stages, and to a smaller extent the drone escort stages. No matter how well you do, the bounty stage is going to take a fixed amount of time to end. On the other hand, most Orb Vallis bounty stages actively reward better players with faster completion times. Exterminate and "collect credits to assassinate", drone hacking etc. all end faster if the players kill stuff quickly. Spy ends quickly if people know the vaults beforehand. Cache ends quickly if players know the right spots to search etc. As players play the bounty stages again and again, they learn how to complete these challenges quickly and efficiently as they progress.
Not so for thermia fracture sealing, which is basically 4 mobile defense stages in a row, each taking 4-5 minutes fixed, and with the datamass spawning in one remote corner of the map. Even with archwing it gets boring really quickly.
While the current suggestions are interesting I suggest the following redesign of the mission to make it more streamlined/ rewarding:
1. Coolant raknoids will spawn on top or near fissures. Killing them will cause them to drop the coolant canister, which can be immediately placed on the fracture. (This cuts out having to run back and forth from the Temple of Profit everytime.)
2. Enemies will spawn as per normal, and the closure will progress as per normal, players will have to defend the canister as per normal.
3. Every time a certain number of enemies are killed (maybe 10-20) a coolant raknoid will spawn and attack the canister. Killing it will cause an additional coolant cell to spawn, bringing the cell to the current fracture will consume the cell and add a flat 10% to the completion meter, similar to a power cell in excavation. (This incentivizes players to actively seek out and kill enemies that spawn instead of waiting for the timer to run out. This also rewards players who are able to defeat enemies quickly with more canisters which can be used either to speed up the current fracture or to use on other fissures, again cutting out the need to run back and forth from the Temple. This should alleviate solo player concerns.)
4. Once the progress is done, the canister is consumed and players get 1 diluted thermia. (I personally feel having to do the same task 4 times to get what amounts to a boss mission key a bit too tedious.)
I hope these suggestions help. DE, if you are planning to make this biweekly like the ghouls you have to make it way faster and way less tedious if you want to avoid burning players out on this event. The double drops during the fractures is really nice and if it's recurring that would be great as well.