Plywood is useless and offers no support, and the oak strips do not help. Build a steel support table beneath it. Anything else will not support that and make it dangerous

Full stop!!!!! and I mean right now. You have an accident waiting to happen.

That base is not meant for ANY solid surface Other than a round patio table with a 42"" diameter top! . I do not care what you laminate to what. Stop it.

If you INSIST on using the top? Build a rectangular "box" steel supports on top/sides. sized at 32" x 36" !!

Box in the corners at bottom, and get some casters on it.!

Second point? Quartz is FAR too much weight for the application you have. The table needs to be EASILY moved!!!

You have no room for feet below with the base. It quite honestly doesn't even look good!

OR?

Take the quartz off, use it elsewhere. Buy a table.': ) OR MAKE ONE.

The table base company specifically says this base is for heavy / stone tops, and this one is rated for table tops up to 48" round. Hence, I assumed this would be fine and plenty sturdy for a 42x46 rectangle. That company also recommends the plywood sub-base epoxied to the stone top. But clearly from my experience it's not working.

https://tablebases.com/k24-semi-gloss-black-table-base

"this one is rated for table tops up to 48" round!!!!! YES ROUND. Hence,"

Your table is NOT round!

A 48 inch surface ROUND on that is a 12" overhang all around the bottom 24 inch base, and even then, I would want steel on that square top which measures EXACTLY WHAT?

Please just start over.

From your link: With a spread of 24" and a weight of 70 pounds, the table base is compatible with square tops up to 42" in size and round table tops up to 48" at Dining height (28").

So you have exceeded the size limit of the base. 42" square is not a 42"x46" rectangle.

Thanks for everyone's comments so far. I do realize the specs said max 42" square top. However, I'm pretty sure that the flex I'm getting is not from one side being 4" longer than spec. That is a fairly insignificant size difference on that size table. Had it been a 42" square, or a 36" square, I'd still be getting that flex. I even got it when I just had the wood sub-top on before putting the quartz on top. The problem is likely just the fact that it's a 10" square mounting plate on a relatively small (~6") column diameter. Even though it's cast iron and can handle 1000 pounds - probably too wide a top for a 10" flange.

Determine if the flex is the mounting bracket by screwing the plywood to it. Add weight, maybe a couple bags of sand and see what happens.

"That is a fairly insignificant size difference on that size table..........."

Really?

Nothing is "insignificant" when it comes to support.

Why do you think it is ROUTINE to have a 12" overhang on a kitchen island?

Because most believe that unless extreme lengths? There is no support issue over 24" depth cabinetry.

Start over : )

millworkman is correct. Plywood isn't strong enough. Square tube steel please.

Are you aaying an entire table base made of square tube steel (get rid of the pedestal altogether)? Or are you siggesting square tube steel can be used with that cast iron pedestal if i ditch the plywood sub-base? (Not sure how id even attach that though. thanks.

It isn't even a good look for what you have in this dining nook!

Draw the walls/ THE ENTIRE nook. Note the bench depth exactly. Do it on graph paper, every last dimension noted, clearly and legibly.

Take picture of where it is located in the whole of the kitchen and beyond.

That's how to get real help. Load it up as a jpeg below

Return the base you bought or use it on the patio?

If this were a counter 15" is the most you could support with plywood. Beyond that it could break and needs steel or aluminum tubing to reduce the flex. A tubing rectangle with cross tubes and with 12" margins could be thru bolted to the plywood with sunken heads.