Celtic or Slavic?

I have been talking a lot about the Germanic - Slavic (and soon we will see maybe even Baltic) people living in Ireland in late Iron age and early Medieval time. I am planning to talk about it some more because i have two more important but mysterious people to cover: Fomorians and Pruteni.

But before i continue, i just want to give my reason why i am so concentrated on this at the moment:

The reason is this:

The Celtic or Keltic languages (usually pronounced /ˈkɛltɪk/ but sometimes /ˈsɛltɪk/)[1] are descended from Proto-Celtic, or "Common Celtic"; a branch of the greater Indo-European language family. The term "Celtic" was first used to describe this language group byEdward Lhuyd in 1707.[2]
Celtic languages are most commonly spoken on the north-western edge of Europe, notably in Ireland, Scotland, Wales, Brittany,Cornwall, and the Isle of Man, and can be found spoken on Cape Breton Island. There are also a substantial number of Welsh speakers in the Patagonia area of Argentina. Some people speak Celtic languages in the other Celtic diaspora areas of the United States,[3]Canada, Australia,[4] and New Zealand.[5] In all these areas, the Celtic languages are now only spoken by minorities though there are continuing efforts at revitalization.
During the 1st millennium BC, they were spoken across Europe, in the Iberian Peninsula, from the Atlantic and North Sea coastlines, up the Rhine valley and down the Danube valley to the Black Sea, the Upper Balkan Peninsula, and in Galatia in Asia Minor. The spread to Cape Breton and Patagonia occurred in modern times. Celtic languages, particularly Irish, were spoken in Australia before federation in 1901 and are still used there to some extent.[6]

Celtic language is the language once spoken in the whole of Europe, but today it is only spoken in Ireland, Scotland, Wales, Brittany,Cornwall, and the Isle of Man.

So here we come to the fundamental problem: Was Proto Celtic language deduced from today's "Celtic" languages like Gaelic, Welsh, Manx, Breton? If we look at the official history of Ireland, we see this isolated Celtic land which for 1000 years only had influence from Celtic Gaul and Celtic Iberia. The first non “Celtic” people to arrive to Ireland were the Vikings in the 9th century, but they were too late to influence the creation of the “Celtic” Gaelic language. So we have absolute right to say that Irish is a Celtic language.

But we are seeing how huge the influence of the central European and South Baltic Germanic Slavic culture was in the British Isles, much earlier than the 9th century and the Vikings. So this then presents a problem: 

Are Gaelic and Galic languages Celtic languages at all? Is this "Proto Celtic" language which we have found in the indigenous languages in the British Isles, just a small part of the real old European Celtic language? Namely is this “Celtic” part found in “Celtic” languages just the part of the real Celtic language, which Gaels and the Welsh, and Bretons incorporated into their languages while mixing with the real Celts of Central Europe, Slavs, Balts and Germans, who are still in effect speaking the Celtic language today in the same area of Europe where it was always spoken? Or were Celtic people just a name for all the white people living in Europe, Germanics, Slavs, Gaels, Balts, Norse? Or were Celts a  mixed tribal union, consisting of R1b , R1a and I1 and I2 people? Something like later Frankish, Anglosaxon and Viking mixed tribal uniouns? Central Europe is still mixed genetically and R1b population still lives in what used to be the Celtic heartland mixed with R1a and I1 and I2 population. Slavic languages of Central Europe are full of "Celtic" words and Gaelic and Galic languages of the Atlantic coast are full of Slavic and Germanic words. We find huge amount of common customs, legends, religious beliefs and practices, superstitions, toponimes, hidronimes, personal names....

Is it time to rethink the whole “Celtic languages” thing?

Here is just an example of what I am talking about:

Pavel Serafimov

Celto - Slavic similarities

Combined analysis of languages, historical sources, burial types, architecture and religion reveals that a part of the Gauls called also Celts were in fact a Western Slavic branch consisting of different tribes who inhabited the lands of ancient France, Austria, Switzerland, Hungary, etc. These people were responsible for the spread of iron in Central and Western Europe and were also the ones to whom the ethnonym Celts was applied for the first time. Unless other ancient testimonies or new archaeological discoveries appear, it should be admitted that Slavic tribes inhabited not only Eastern, but also Central and Western Europe in the deep antiquity and were strong, highly developed people, who influenced many others. Novel evidence of Slavic presence in Western Europe and British Isles is presented in this paper. Scientific method demands that the opposing arguments and theories have to be considered. Counter evidence and counter arguments are welcome….

Or this:

Pavel Serafimov, Giancarlo Tomezzoli

Slavic influences in the Ancient Gaul

It is common opinion between the scholars and the people that the ancient gauls formed a compact set of Celtic tribes speaking the gaulish language or similar varieties of the same one [1]. The gaulish language also called Classical Celtic had practically nothing in common with Insular Celtic; it was very close to the Italic group of tongues and had grammatical forms similar to those of the Proto-Indo-European model [1]. however, the publication in a recent past of relevant works has animated the debate about the slavic cultural and religious influences and about the slavic presence in the ancient gaul. With this paper, after having reviewed said relevant works, we analyze in more details some origins of these influences and presence so as to introduce some more arguments and evidences into the debate.

Without knowing how strong and how long the influence of the Central European cultures which reached Ireland and Britain via South Baltic was, the above claims would have been absurd. Now they are to be expected.