The sponge is too fine!!!
Choose a sponge that easily fits that that plastic frame/base, and proceed.
Your definitely doing the correct thing as for filtration, just swap sponges.
They may describe the porosity as a "PRO" version or coarse.
Below, I'm approaching a half dozen of the same filters, but they are the Cobalt MJ900s.
The Cobalts seem to be the same thing at a glance, but have a tighter fit and finish than the Marineland MJ when the parts are handled and not just seen in a photo.
When the chart is seen on the MJ400 vs the 600 vs the 900, vs the 1200, the flow-to-watt ratio on paper has the MJ900 winning.
The MJ1200 is near 20 watts and there are other pumps that can do better for that wattage.
The 900 pushes a lot more than what you are used to, BUT if you use a Tee or a larger output, elbow or screen, then the water actually is diverted differently than a high nozzle-like flow.
It's like aiming a house fan at pricker bushes, and not so in-your-face abrupt.
Dampen the output if needed, don't sacrifice the cycle turnover rate.
Either, I'm doing it wrong, people are afraid of change, or they may like the air pump noise and splatter from bubblers popping water stains all over the top of the tank.
Whatever the reason, your heading in the right direction in my opinion.
If you still like air bubble and hydro sponges, you can add an umbrella of sponge at the top of the rising bubbles to catch the popping splatter of messy bubbles and tie it off as plants are added to hide any eye-sore of equipment once the design is complete and you are satisfied.
The pics below are some of my history of changes and quarantine quickies while I needed to transfer tanks and fish.
The Eheim SKIM350 works wonders at the surface in addition to the underwater Hydro-Sponge/MaxiJet combo your working on.
one more point to make:
BTW, in your photo the exterior of the sponge has broken down mulm and other random stuff clogging the pores.
The open porosity sponge will take in those particles and break them down better with more nooks and crannies.
The mulm (broken down detritus or poop) will still be there, but it will be a factor of your particular fish load of when the sponge needs to be extracted and dipped in water change water to wring out.
Mulm is ok, just not on the outside of your sponge clogging it.
For example, if a deer dies in the woods....it smells and is breaking down.
It will soon be nothing but teeth and bone and almost harmless to the situation.
Mulm is harmless broken down to the last bit, but still there as a physical thing.
It's the same as a bag of bones stuck in an intake of a fan.
No huge issue as for smell, it's just in the way of flow at that point as well as not the proper or ideal way to run.