No it wasn't. 2e was a rework for the playstyles that were common in the late 80s, post the departure of Gygax, and post the Dragonlance Saga. It took some of the more useful things from Unearthed Arcana (whether weapon specialisation, specialist casters, or non-weapon proficiencies), dropped some of the devils and demons - and changed the basic playstyle from a dungeon based game where you were adventuring for loot and directly got XP for GP to an encounter based game where XP for GP was, rather than the driving engine for the players, demoted to an optional rule and characters were rewarded for doing things suchj as casting spells.
It was more than a simple cleanup and cut down. And if you approach both games cold they are very different
To THINK that everyone played it as a Dungeon game, even in 1975-1983 is someone who DID NOT PLAY D&D or AD&D back then.
Period. Dot.
It wasn't a Dungeon Based game...even when the 3 LBBs came out. Trying to prescribe a SPECIFIC gamestyle on everyone who played back then is inherently misunderstanding HOW the game was played and WHAT the game even was.
I saw all sorts of different playstyles and ways to play. I saw how the old guard played (and believe it or not, there are times I don't think Gygax actually used the XP as per monsters or GP given as some would believe, but tailored it more towards encounters and game sessions...BIG SHOCK!!! I know).
The 2e core rules basically compiled 1e rules into a core rule set.
AS for Session XP, that was originally alluded to in the 1e DMG near the end of how XP was awarded. It gave out numbers and how it was, and then finally states that the actual award is DETERMINED by the DM. It then, in the training area, explains about how the characters acted can determine how much of a reward a DM may actually award. This was further extrapolated upon later in articles and other such arenas.
This was NOT a new item introduced in 2e. By the time of the early 80s it was actually quite regularly seen among D&D groups.
In the 2e DMG, When it is explicitly stated how players earn XP it gives two methods though (even though it suggests DMs determine the awards in the short sections prior to it). Thes are individual and group rewards, with the first of these identified as the XP gained from Killing monsters (same as 1e, though the actual XP granted is greatly simplified in how it is presented and thus different by a strictly numbers sense than it was in 1e).
It then goes into more detail on Story awards (that the amount should NOT exceed that XP gained from killing monsters. This was probably put into the books because by the mid 80s some groups were giving LARGE amounts of XP at the DM's whims in some groups rather than from book values. It specifies that a story award at maximum should award no more than 1/10 that needed for the next level.
The other caution given is in regards to XP for gold awards. It had been noted by several authors in Dragon and other locations concerning "Monty Haul" games (which is ironic, as per the rumors, Gygax did both Monty Haul games and DM grants a ton of XP games...so both of these ideas could be seen as anti-Gygaxian ideas in some ways). The specific warning about XP for gold, which is given as another option for those to gain XP in AD&D 2e is that "One XP can be given per gold piece or equivalent, found. However, overuse of this option can increase the tendency to give out too much treasure in the campaign."
This strongly suggests that you haven't looked at your 2E core books in a long time.
Seeing I played it last night...I'd say you are EXTREMELY wrong on that suggestion.
This biggest problems I see in some of the assumptions being made and those trying to say 2e is not Old School is that they do not understand how 1e worked when it was the primary form of AD&D, nor how it was played in general. They ascribe a specific way of how they saw it as played, and assume EVERYONE played it that way, when it wasn't even played that way in the adventures put forth in many instances (for example, Temple of Elemental Evil obviously has some great dungeons, but there's also a large part that happens in the overland, the wilderness, and town of the area).
It's like those who try to say 2e created THAC0, not understanding that THAC0 has been around since the 1e DMG and there were adventures that actually also presented it and used it, as well as groups that started using it early on as well, just for simplicity.
The final nail in the coffin is (for those of us who actually were AROUND and PLAYED it back then) that 1e was EXPLICITLY grandfathered into 2e. Any 1e rules that you wanted to play were stated to be allowed with the 2e rules if you wanted (as if we actually needed that permission...we didn't. But...they gave permission anyways). That's how we played Dragonlance in 2e originally, with the old Dragonlance modules and rules with 2e.
I just entered a 1e spell into a contest here on ENworld (and apparently NO ONE noticed that it was actually a 1e spell, which tells me how many actually really look into their books and are familiar with the layout of 1e these days). I've been in my 1e and 2e books and play both these days. Sometimes I wonder how many groups of us are actually left.
I ADMIT, I'm not really into the OSR scene (my take, is if I have the rules for the original games they are based on, why should I play the copycats rather than the actual game itself?), but for those that are, trying to say AD&D 2e is not Old School seems like an absolutely ridiculous claim to me. This coming from someone who actually still plays those games, rather than the OSR games that are based on them.