Ok first some of you misunderstand what I'm trying to say about works such as the Tain. I never said the Tain consisted of stories that were 100% historical fact. What I AM saying is the Tain IS without a doubt thought to be much older oral tradition that was actually put to paper by christian monks in the medieval period and warped a bit to demonize/twist the original pagan ways, to make christians look better than savage pagans.

Now, "Oral Tradition" doesn't mean Historical events. It means that these heroic stories were passed down through the generations by mouth, much as the Illiad is thought to be. Legends and myths are often based at least somewhat on historical fact, then embelished to be more heroic/grand/etc. If the Irish were keeping stories of champions who had war chariots for centuries and we know their neighbors used war chariots, then is it really such a stretch to believe that war chariots were actually used by the ancient Irish? It doesn't mean that they had magical weapons, the ability to cleave the tops off mountains, and sorcery. There are other stories that involve characters in the Tain that are dated centuries earlier than the Tain was written down.

If you read an ancient tale about a warrior who always rode a black horse and defeated many enemies with his magic sword, would you think that there was never such a warrior? Or would you instead believe there was a warrior who had a higher quality weapon who had killed men in combat? Again most legends are based partially on fact that is then embelished/exaggerated to be more spectacular.

Now, concerning Ireland's terrain, it's recorded that Irish warriors of the Dal Riada used war chariots in Scotland and many parts of Scotland are very similar to the terrain in Ireland. Concerning bogs, many bogs that exist today are man-made for many different reasons, such as deforestation and current figures do not necessarily reflect what figures would have been like in the Iron Age. Concerning the comment regarding the usage of tanks on the terrain in question, tanks weigh many tons and chariot very likely wouldn't weigh more than a 150 kilos. That's not a very good comparison, instead why not ask if wagons or coaches were ever used in this terrain? We know they were and they are still used today.

Finally, on the differences in the description.
Original description
1. Goidilic tribes used some chariots.
2. Goidilic tribes used some large horses.
3. Smaller horses were adopted in favour of larger ones.
4. Reasons for favouring smaller horses rely on the terrain and climate in Ireland.
5. Larger horses and chariots couldn't move as swiftly as smaller mounts in wet and rocky terrain.

Riastradh's suggestion
1. Goidilic tribes used some chariots.
2. Goidilic tribes used some large horses.
3. Smaller horses were more widely used than larger ones.
4. Reasons for favouring smaller horses rely on the mobility and cost in comparison to chariots and speed, mobility and cost in comparison to larger breeds.
5. Larger horses couldn't move as swiftly and chariots couldn't maneuver as well as smaller mounts in addition to smaller horses being better suited for use in dense forests and broken ground.
6. Ponies were superior when charging an enemy's flank, and were often used in hit-and-run attacks

Hope this clears things up a bit more.