Big question with some variables included.
Do you need a spod/marker rod?
I've added in the bracket marker as many spod rods now do both, use as a marker rod and spod rod.
When I was fishing the 2 acre Brackens Pool at Nazeing Meads I went 3 years without using a spod (rod), however my marker rod was used for precise location of the gravel, which if you missed, instead of fishing 7feet, you'd be in 22feet of water.
My baiting was solely with stringers and mesh, as much as 30baits on a stringer, and I caught plenty.
That is probably the last time I can recall not using a spod or Spomb.
Now what makes up the variable, is the size of waters, what is working and what you might do differently.
On a 4acre water, say going up to 10 acres, fishing boilies only, I don't think that you need a spod, almost every spot can be reached by catapult or stick, it is when you add in pellets and particles and mass baiting that the spod becomes essential, as anything above 30metres takes out cattie range.
Are you going to fish boilies only, or do you need particles?
Can you hit your spot with numbers of solid bags? It is different from most other people's fishing, it could be your edge.
That might be your answer there.
For a few years, my 3rd carp rod was my marker rod, it was 'ok', but not perfect, so I bought a marker rod and used braid. The feel was totally different, from gravel feeling flat, I could sudden feel 'the bounce', from weed feeling steady thick, I could feel pull back as it broke free. Braid may have been a lot of the answer, but the right tools for the job help.
Next question why 3.5lb TC rods?
On waters up to 4acres I wouldn't go above 2.75, even banging out big stringers or bags. I only use 3.25 TC rods on 45acres.
The test curve does not equate to how big a fish, or how powerful a rod is, the action also needs to be included, but higher (say above 2.75lb ) are designed primarily for long casting.
One 2 acre water I bailiff, with carp to over 20lb, you would be asked to leave with those rods. Other rules include No leads above 2oz, and hooks no bigger than size 10.
When I fish there, I don't even take my carp rods, but use my specialist rods with a 1.75lb TC and believe me I've had many carp over 20lb and it's more fun on the gear.