it's not just about the power output per say, the S220 if dumping at full that yes will allow you to get great images is taking 2.1 seconds to recycle which can be too slow when doing action shots. More powerful strobes that are dumping at say 2/3 for the same required light output that can recycle a few times a second at that power allow you to catch action shots.
We aren't always taking action shots, but in 3 decades plus of shooting underwater, my biggest regrets are shots I missed because of slow recycle times more than even backscatter (and now we have tools like backscatter eliminator and other PP tools available now). We also have strobes that are amazing for recycle time, they really are. I have a couple dozen strobes around here, YS-27dx, YS-90DX, YS-110, YS-50 and 60, YS-120', SB-105, YS-D1, YS-D2J, UFL-03, YS-01/2/3, Ikelite DS-125, AOI UCS-Q1, Backscatter MF2 and HF1's. I have shot a few more types and yeah, been a S&S more than INON fan but also have had good luck with S&S even when many others..not so much. Truth is the DS-125's of which have a half dozen have been my go to when shooting faster and I know I will be, the YS-D1 and UFL-03 depending have been my go to travel rig (I REALLY like MFT for travel and keeping it small, but then again pics are normally a side event "if I get time" to my dive travel than the main attraction), but are SLOW to recycle and have missed MANY shots because of. The AOI/Backscatter strobes are eye opening and technique changing in their recycle speed, as as some of the many new to market strobes that have come out lately. Truly, underwater photographers have never had so many great choices, and pre tariffs never so cheaply..YMMV now on $.
That said, the old and good advice of buying a better strobe than you think you need now if there is any chance you may stick with UW Photography because strobes you can use for a few "generations" of gear changes still applies but is a bit more complicated now as well because now we have not just wired connection variety but also optical cord variety (manual or TTL, and if TTL what type of TTL for what brand camera) and yes even wireless connection for strobe use on the market (look at Marelux) and that will frame things I suspect (right now it seems to be like when optical came out, showing the promise and working most of the time but not always, it will mature I suspect). Will getting 2-4 generations of cameras using the same strobe be a "thing" in future? Harder to say.
Example, I really do mostly shoot MFT the last decade. I got rid of a Canon 5D Mkll in Ikelite housing when I started to shoot the Oly Em5. The quality was close enough, macro was better really and the size saving was huge making the change. Have went thru various gens of Oly and the size has creeped up however. RC TTL is awesome, so that shaped some strobe decisions and really, recycle speed has been what I looked at last couple years that can make me happy. The DS-125 are faster than all those old S&S strobes but between the size/weight I hardly ever use them unless is a specific reason I know will be best tool for a dive. Enter the HF-1 and they are a heck of a great solution that are however slightly bigger and heavier than I want for travel but can live with it given all other advantages. Just recently however I ended up with an Ikelite D850 housing w/ ports (for WA, which is what I would use the higher res of a D850 for, macro, I am still firmly in the MFT camp) at almost a gift price and the HF-1's won't work unless I get the manual optic converter for the housing, or do I go ahead and get the Nikon TTL and use my old DS-125's again? I suspect that will be the case, even as I look at the DS-230 and see their limitations in many ways but also how darn good they are at what they do in an Ikelite system. Old school but also fast, powerful and simply beautiful colour temp and light output. I mean, it's a big camera/housing setup and will be taken only for deliberate shooting diving and having as many tools in toolbox as far as what strobes can do is kinda making sense. I know I can make and be generally happy with the DS 125's, even as old as they are, but I am feeling I will be happier with 230's, even if logically I KNOW that I would be spending a lot of cash for ability over the 125's that I will be using less than 5% of shooting at best, but maybe I will also place myself in more situations where that type of shooting requires it .. hard to say. But finding myself contemplating different strobes so soon after getting strobes I really have liked so far but are not really very compatible with the "new" (used) system is a bit annoying.
Anyhow, it isn't just about power when you get a powerful strobe.
