Pumps like this are quite sensitive to how high they need to lift the water.

Personally I'd suggest doing a test on the pump/sprinklers first. Just connect the pump and existing pressure tank to a 3/4 hose fitting, run your hose out to the sprinkler, and make sure the pump and well can run your sprinkler. This lets you know if new piping will fix your issue or not.

If the pump does not keep up to a sprinkler, then either it's lifting beyond what it's rated for, or it's badly worn. Some wells tend to pick up a little sand, and the sand chews up the impeller. Or if the pump ran dry for a while.

A larger pressure tank reduces how often your pump needs to cycle, but if the pump can't keep up then the pressure will just slowly drop off. So if your pump just runs (doesn't cycle on/off) the whole time you have a sprinkler going, then a larger pressure tank is not very useful.

Bypassing the filter and water softener will help for sure, and save you money. No point carbon filtering and softening water for the garden!

Avoiding the filters, and using a 3/4 line would probably be all thats required as long as your pump is sized appropriately.

I feel that 1-1/4" is overkill for a sprinkler.

What hp pump? How deep of a well? How far from the pump to your house?

Not going to last, as mentioned by other commenters, but if you just want a fix for a year or two:

Rent a pressure washer, clean off the surface, all the cracks.

Make sure the surface is damp. Mix up a bag of ready to mix concrete, pour it on, level/spread it (screeding) with a 2x4. A large drywall trowel or something similar can be used to get a nicer finish.

About a $15 'fix'. And as the others say, in a couple years it will probably break apart.

There are the three drilled and threaded mounting lugs, but I see two more lugs on the back with no hole. Willing to bet they have screws inside. Maybe they will be holding the guts in.