The sledge or stagbreaker are still good for things behind closed doors. Even the atgier's spin can help for that but doesn't have as much range.

In many of the mines I've been to there has been a hole in the floor close to the entrance. Sometimes you can aim arrows down there. Ooze bombs and fire bombs are great for this too. It can take time to whittle down a soldier this way, but better that than going toe to toe.

Soldiers are big enough that sometimes you can get them stuck or blocked. The seekers have no problem getting up stairs, but the soldiers can't manage it. They also can't get inside those small hidden rooms. If possible look for a way to get them terrain locked.

Baby seekers go down easily with the atgier, or ooze bombs or any AOE. I know they're not a big threat, but if you also have ticks and other things at the same time it adds up.

Don't stand and tank if possible. if something has aggro, back up and fight it in a previous cleared room to lower the chances of having others join in. Also makes it easier to recover your corpse if it comes to that.

There are no spawner piles in the infested mines. If you see a whole lot of seekers, it's because there's a huge room, or several connected rooms in front of you. Don't storm ahead trying to find the spawner. Be patient and try to clear them a little at a time. (I did this once when I thought the numbers were too high for there not to be a spawner. And of course dying after charging in makes it nearly impossible to get your corpse back. I ghosted around to check and nope, no spawners, just a giant cavern below me.)

It might take more than one try to clear the entrance. If in doubt, back out, heal up get rested. Having a fire or portal out there helps. If the seekers get into the entrance they might even kick you out, which is not necessarily a bad thing.

Slow and steady, one bug at a time. (Now if someone would tell the bugs that.)