I get this impression that history is portrayed as something violent, brutal, warlike and oppressive while prehistory is a peaceful and awesome sounding Neolithic Revolution in technology etc. focusing on production
Is it because historians focus on written texts, which is often a letter like "I declare war on yo ass lol" and prehistory is mostly interpreted by archeologists who in their diggings they find mostly tools and stuff, so they focus more on peaceful productive technology?
Generally if sometheing is called an Object Culture is it prehistory and archeology and if a people has a name it is history?
I mean, when something is called Funny Looking Large Clay Pot Culture by, I presume, archeologists, do historians link it with history and say "oh yeah that is ancestors of Germanic tribes Tacitus described"?
Is there any reason to see European prehistory as something nicer than Ancient history? Like where Bronze Age and Iron Age slowly flowed into actual history, did violence or oppression increase or decrease? Would life in the La Tène culture be more brutal or less brutal than what later in history was called Celtic Gaul, pre-Roman Gaul?
The technical distinction is very simple: prehistory is the human past before the invention of writing, history is the human past where written records are available. In practice this means prehistory is the domain of archaeologists (people who study the past through material remains), and to a lesser extent geneticists and linguists, while history is open to both archaeologists and historians.
That difference in the type of evidence we study has all sorts of effects, some of which you've mentioned it. Archaeologists make up names for peoples based on artefact types or geographical locations because we don't (can't) know what they actually called themselves. We also concern ourselves more with technology, material culture and long-term change because those are the research questions our evidence is best suited to. Still more differences come about because archaeology and history have developed as separate intellectual traditions, with different goals, questions and points of reference. And scholarship is fundamentally a social endeavour, so never underestimate how much working in different buildings and going to different conferences changes things!
As for violence, you're absolutely right that many people have been influenced by the idea that prehistoric people lived simple, peaceful lives in harmony with each other and their environment - the old myth of the "noble savage". At the same time, there's an equally powerful idea that prehistoric lives were "primitive", "nasty, brutish and short." Thankfully prehistorians have long since dropped ideologically-derived assumptions like these. But figuring out how much violence there was in prehistory is a really tricky problem. The physical evidence can go either way: you find an axe - is it for splitting logs or skulls? A rampart - to keep cattle in or enemies out? A violent death - ritual sacrifice, murder or warfare? And nobody agrees on whether we should expect people to be violent or not: is violence "human nature" (Richard Wrangham Demonic Males, Lawrence Keeley War Before Civilisation), or only found in specific social circumstances (see the recent edited volume War, Peace, and Human Nature)? Ultimately I think if you asked most archeologists if prehistory was violent their honest, gut answer would be "it depends" or "I don't know". You can't generalise too much; prehistory is 2 million years of human lives all around the world and for a lot of times and places we simply don't have the data.
You are not unique in making this observation. It is in fact the entire premise of Otto et al.'s 2006 book 'warfare and society [in prehistory]'. Up to the 60s or so, people might have had the reverse impression: prehistoric archaeologists were constantly talking about invading peoples and conquering tribes. However, from the 60s to the 90s it was much more popular to instead focus on the things that you describe, food production and house architecture, and explain them from this harmonious social perspective. From the 90s, people have focused more on religious perceptions and lifestyle, but again without regard for violence. It is only in recent years (Vandkilde in Otto says since the Yugoslav wars, in my opinion since 9/11) that warfare again is a valid subject of research and is regarded as a primary motivation for social change, but it takes some time for the schoolbooks and museum exhibitions to be updated.
Outside of archaeology, the disciplines have had very different histories. In anthropology, the 'problem of war' ((in)stability in society) was always a concern, and much ink has been spilled in seeing 'culture' as a way to channel and guide natural tendencies to violence. From this perspective, history is actually more peaceful than the past. The primary advocate of this perspective is Keeley's 1996 book 'war before civilization'.
The recent re-appraisal of violence in prehistory does not mean that we go back to the interpretation that our 'ceramic cultures' (such as 'Bell Beaker Culture) reflect political units like 'the Frankish kingdom' or 'the Roman Empire'. Rather, we would acknowledge that we can not (or with great difficulty) see the political units in prehistoric war, unrelated to their material culture.