I also ran as Warden/druid these last few days and I never had that problem. Oak Walker already has a 75% aggro decrease and in my case he never had aggro, except face aggro, which the tank easily took/spotted.
Greetings.
I have the same problem when run dungeons as Warden / Druid. Also I was testing him in atlas defense duo with healer. And it's a dissaster, because I had to summon Oak Walker on every wave of mobs when I was using aoe skills under Power of the Oak buff, mobs targeting Oak (because he also attacks few mobs with Sepal Stab) and he just dies. The same happens in dungeons, Oak dies and I lose half of my damage + it destroys tactics on bosses, if boss gone in immune phase tank can't even take boss till Oak not dies. Very annoying to play this class because of this.
Also I tested it solo in 100 lvl dungeon hard mode, twice killed 1st boss and both times my Oak Walker was tanking him, not me, so he does more aggro than I do. Please, fix this issue, decrease his aggro
The Oak Walker still have -75% aggro. If you are at -90% and doing something alone, you should increase your aggro. Tanks also need a job. Decreasing more aggro would destroy the need of a tank in some was.
I, as a tank, never had a problem with warden pets aggro since it is at -75%
Kind regards