I've never played as an Orc prior to Skyrim so forgive my ignorance. I have always seen Orcs as my least favourite race due to the stereotypical warhammer / warcraft style of Orcs. It was only due to the start up screens on Skyrim and an added inspiration from the Dothraki in GoT that I've come to really show an interest in them.

The question that bugging me is "have the Orsimer always been tall or is it just the Skyrim height slider?".

I was always of the opinion that Orcs were transformed to be ugly and part of this was to make them shorter and stocky (the pig children as one in-game book calls them). Back in previous games, I thought Altmer were the tallest but of a more frail frame (which was made up for in a bonus in intellect), Nords were next tallest but with a naturally physique frame (bonuses on stamina & endurance etc - example I guess would be like world's strongest man competition, wrestling etc). Redguards were next in height but built more for athletics (running, boxing etc), Imperials, Bretons, Orcs and Dunmer I thought were all of a similar height. Orcs being stockier and strong while Bretons being the opposite and excelling more in mind and intellect. Last was the Bosmer who came in slightly shorter.

Am I kinda correct in any of my understand and has things been changed? Or did I just pick the information up wrongly at the time and I've just carried it along with me?

I always figured the Orcs were about the same height as the Dunmer, just bulkier. In Oblivion, the Altmer were the tallest while the Bosmer were the shortest. Orcs were about the same height as Imperials if I remember correctly.