We have no idea when populations of different haplogroups started to mix heavily with one another in the Near East. Based on ancient European Neolithic samples, it looks like Near Eastern Neolithic farmers only belonged to G2 and T1a, although if T1a is there then J1 will also turn up as the two are intricately linked.
Obviously R1b were cattle herders, and the simple fact that R1b-V88 expanded from the Near East to North Africa is proof enough that it was really a Neolithic lineage too - but one that was clearly separate from G2a as R1b-V88 is very rare in Europe today. We still can't exclude that the R1b1* from Neolithic Spain was V88+ as they didn't test for it. If so, it is not impossible that it came through North Africa, which would explain why no R1b-V88 has been found in Neolithic sites outside Iberia.
To summarize there were at least 3 distinct Neolithic populations from the Near East, who may not have mixed with one another for several millennia:
1) G2 cereal farmers
2) J1 & T1a goat herders
3) R1b cattle herders
There might have been a 4th group made of J2a, but I still don't know where they originated. I think they were rather Near Eastern HG during the Neolithic, and might have thrived from the Chalcolithic onwards, just like R1a.
Even when we look at Early Bronze Age samples, it looks like intermarriages between locals and newcomers was not very common. I think it is especially from the Late Bronze Age and Iron Age that we really see frequent intermingling and a homogenization of the regional populations. It makes sense from an anthropological point of view too. The Neolithic was all about extended families and local communities. The Bronze Age was extremely hierarchical with a ruling elite that didn't mix much with the rest of the population (except through concubines). But the Iron Age was much more egalitarian age, where most men could afford cheap iron weapons, unlike the extremely expensive bronze weapons. Many historians think that the great upheavals of the East Mediterranean c. 1200 BCE are linked to the adoption of iron weapons by the populace, who then overthrew their oppressing ruling elite.
Neolithic farmers ENF were most expansionists of their age, unlike Hunter Gatherers who were rather local isolationists. Wherever we test HGs in certain region, they belong to one haplogroup or handful of similar clades. On other hand ENF in Europe incorporated local HGs haplogroups rather early during their expansion becoming EEF. The best example is Neolithic genetics from Hungary where we can find not only farmer's hgs but also HGs like I1,I2 C, F, H2. For few tested Neolithic Hungarians we found 4 or 5 distinct haplogroups. And we know they were not HGs but real farmers with farmer autosomal DNA, just hunter gatherer hgs. This multi Y-DNA mixture is a signature of farmers in Europe, after couple of millenia.
I would be very surprised, if this situation was different in Middle East. I suspect ENF, at the end of Neolithic, incorporated few HGs haplogroups around Middle East too. Therefore they became Y-DNA mixed population by the end of Neolithic, before copper age.
According to this scenario, if Yamnaya R1b folks came from Middle East farming horizon, as farmers/herders, they wouldn't be pure R1b anymore. Instead of seeing only R1b clades in Yamnaya we would have gotten also G2a, J2, J1, T, E and more, bunch. But it is not the case at all. We have only R1b and mostly of the same clad. By this token I think they look like HGs folks, but with half Armenian like admixture. In this case, I suspect that, if they came from somewhere, it wasn't too far away, and definitely not from Middle East. I think this Armenian mix is from close by Caucasus area, and it is Caucasus admixture. Perhaps this admixture came with acquired women only but men being from Samara afterall.
Farthermore, there is a strong case that Caucasian admixture came to Yamnaya before Gedrosia reached Caucasus. On this chart below we can see that Yamnaya admixture still exists today in modern populations of Lithuania and Belarus, the regions which have no Gedrosia whatsoever. In such elevated levels of Yamnaya admixture, over 50%, there is no chance that gedrosia didn't show up in these populations, if it was present in Yamnaya dudes.
In this case the 50% Armenian like admixture has to consist of Caucasian and some ENF admixtures, I guess.