I think you've been given some great advice--find ways to do all kinds of explosive squatting and pressing movements and keep working your engine especially with full body movements like the wall ball and thruster.
Here are some other ideas, taken right from an article by Coach Glassman referenced in The CrossFit Journal. There was recently an article titled "The Glassman Chipper" suggesting athletes and coaches go back and read some of the old, original classics. One was "Strategies for a 7 minute 2k on the Concept 2 Rower." Glassman goes through some different training strategies to try to get there, distinguishing task priority and time priority workouts and also combining the two and factoring in pace. Here is a link to the article:
Applying the suggestions to a faster Karen, as opposed to a 2k row, maybe pick an attainable goal time for Karen and design workouts to try to meet those numbers--let's say you go with 6:00 even with the idea that you could then dip just under it into the 5:00s. A 6:00 Karen means you have to average 25 per minute for 6 minutes.
So what are some different workouts to design to get there?
1. Hold 25 wall balls a minute for as long as you can, working to increase how long you can hold that pace over time until you can get to 150. Each time you try the workout, attempt to extend how long you can hold the pace.
2. An EMOM was suggested above--but I will add some specific analysis to it for you in terms of numbers. Right now, at 6:38, you are just above 22 walls balls per minute. Maybe try to go up to 23 or 24 per minute, then rest the remainder of the minute--it would probably be short but maybe beneficial--and see if that pacing strategy gets you closer to 6:00. You might find you are actually faster already just by targeting a more manageable pacing strategy and limiting rest. Over time increase the number per minute.
3. Another way, a suggestion by Glassman in his article, is to really combine task and time priority into one so you work to maintain a pace. For example, do 25 per minute wall ball pace for 6 minutes, but start by building in a short rest--maybe 20 seconds as a starting point--and go again until you get to the full 150. Then start shortening the rest over time as you improve until you essentially eliminate the rest.
Those are some other ideas on wall ball workouts, of course stolen/adapted right from the article. But great ideas nevertheless.
Just remember to have fun with your efforts to stay atop the leaderboard... ...someone better will always come along especially when you are working to keep up with the young crowd.