I started with the fact that carbonates was needed to reduce rhe bitterness of my octoberfest to make it more like the ones I've tasted.
I don't think I've ever seen it suggested that adding carbonate reduces bitterness. Sulfate, yes, but not carbonate. As noted in the previous post at proper mash pH carbonate is converted to gas and driven off. At mash pH carbonate is not a problem because it is gone. The problem with it is that it prevents the mash from reaching proper pH.
Adding so much carbonates raised the mash ph so high it was off the chart for the test strips. Would this have produced a good beer?
No, quite the contrary. High mash pH is detrimental. That's why no reliable spreadsheet, calculator or brewing software package will advise adding chalk unless the need for it has been verified with a pH meter reading.
I added enough lactic acid to bring the ph down to an acceptable range for proper mashing.
And in so doing saved your beer.
Now if you measured 5.3 with test strips the actual pH was probably 5.6. This is marginal. There is a fair chance that the beer would be better still with pH a bit lower say 5.5 but 5.6 is OK. But you cannot rely on strips for pH measurement and you cannot fix their lack of accuracy just by adding 0.3 to their readings. Accurate pH readings can only be had with a good meter.
Did the acid and carbonates cancel each other out so the chalk would not have any effect? On paper they may. In the actual process of mashing they did not because the hops were drastically mellowed and the maltiness was much more pronounced jush as an octoberfest should be. The only changes I made to the recipe was the additation of the chalk and the lactic acid. I did not add any lactic acid in my previous attempts at this recipe because without the chalk the mash ph was acceptable.
I cannot say exactly what happened here but I can advance a hypothesis based on my and other brewers experiences. When beer is mashed at high pH the result is drinkable enough and perhaps even good. If the same recipe is mashed in the pH 5.4 - 5.6 range all the flavors become brighter and the beer is noticeably better. This fits your description of what happened. I hypothesize that as you didn't use lactic acid for the early batch(es) the mash pH was higher than the optimum range. A reading deemed acceptable with pH strips confirms that. You got the idea that adding chalk would help (I'd like to know where that advice came from) and the pH rise was so dramatic that it frightened you into adding enough acid not only to remove the carbonate but to get the pH down to 5.3 on strips which is a probably 5.6 in actuality which I'm guessing is actually lower than you had before.
would adding lactic acid alone to the mash reduce the bitterness and allow the maltiness to stand out more which was what was needed for this recipe?
As a general statement reducing the pH to the proper range will noticeably improve the beer and it definitely does that in part by amplifying the malt and yeast flavors. As far as reducing bitterness goes, getting the residual bicarb down may be of some help and hops isomerization is lessened at lower pH so a combination of those two effects may be in play here. Also your sulfate is getting up to the point where it may be damaging to fine hop bitterness. So you might want to cut 1:1 with RO to get that sulfate down to half its current value.
All of the research I have done indicates that the carbonates is needed for that
As I noted earlier I am curious as to where you found that. As a general rule carbonate/bicarbonate is bad and brewers go to great lengths to get it out of their brewing liquor. Dark beers came about because the acids in malt remove bicarbonate. Light beers are brewed with waters which don't have enough bicarbonate to do serious damage.