This is WAY outside of my experience. Even looking at encounters on LEB and such, I have never ever seen this. This sounds like extreme examples.
LEB?
We have a Come and Get It fighter paired with a Swordmage partner in our home game and they are not able to do this.
How many rounds does it take you guys to kill stuff? That may be a lot of it, too. How about how much control you bring? I can often lock things down pretty good for a couple rounds, but then we're out. But that's plenty long enough to drop things down to just a few key people. The swordmage also has interrupt powers where he teleports people out of attacks.
In the example where my paladin prevented anyone else from needing to spend surges, I was backed up by a wizard with storm pillar & grasping shadows to funnel enemies and chilling cloud to give them -2 attack. I'll say right now that a shield + plate pally at low level with an extra -2 on enemies' attacks is in _very_ good shape, and 7 radiant is a very big deal against 1st-3rd level enemies.
I did a different run with him once where I didn't have to spend any surges, cause the DM often did not follow mark, or missed me (nothing like sanctioning 3 halfling slingers and then not getting hit, poor DM), or in one combat I got 10 free healing from a shaman daily. Mind you, I did soooo much damage from sanction, I was outdoing the strikers. And the -2 attack helped the enemies miss a bit, and he did most of his damage from FRW-targeting area attacks, so I'm not sure it really worked that well for the DM.
I suspect this has more to do with your DM and how he creates and manages encounters than with the abilities and tactics of the PCs. Sorry, but it just doesn't make sense that 8 encounters could occur and only one PC other than the defender used a single healing surge. Were the rest of the PCs in a different county?
If we'd had to rest after the final encounter, I'm sure they'd have used some,but... that's pretty close to what we did, yes. Which is part of the point, right? We were playing an all changeling group that was bluffing and sneaking our way in as much as possible. We had two other people doing melee, one of whom needed to be in melee (barbarian), the other of which didn't really (rogue) so would get into melee later. I was sanctioning as much as possible, especially early in the fight, including doing ardent sanction charges using a badge of the berserker I'd gotten.
The first encounter actually started, for some obscure reason, with me completely surrounded by enemies and the party like 16 squares away. So, yeah, they were fine.
The next couple encounters we initiated.
First one was against a group of rogues gambling. So I went to go gamble in the middle of them to provide a good target. Some went before me, attacked me, cause hey, flanking me. Then I valorous smited.
The next one I went first, moved, challenged, then ardent charged a guy next to him, then valorous smited, to sanction the entire rest of the group.
I mean, rest of the PCs are 6-10 squares away and you're paladin sanctioned, that's a good reason to hang around.
Later storming a defended position, not much I can do to keep the archers off the rest of the party. So, they used a lot of terrain and gave them penalties to attack, until we could nail them down.
Sneaking around, we managed to avoid an ambush and set up a corridor fight against a huge mess of mostly melee guys... so challenge one guy, ardent strike the other, barbarian is beside me, they're at -2 from chilling cloud.
So, yeah, I took extreme risks to multi-challenge lots of guys and most of my party was far away. And it worked out that they weren't in much danger as a result.
The fighter event was more normal.
First fight: Spread out area, I took half, the swordmage took the other half, cleric 'turned' an elemental to force him a bit aways. We obliterated one guy, I left another guy with the rogue to go deal with more interesting things and he missed the rogue, then the swordmage teleported someone else that was getting attacked, and then that fight was locked and set.
Second fight: Odd warehouse with sorta corridors, lots of cover, lots of sneaking and sniping. We do mass concentrated destruction in the center to drop about half the guys, then again I cover one half, he covers the other half.
Third fight: "Ambushed" we've got guys on all sides. Cleric gets surrounded in back by a few minions and one real guy. Swordmage bears most of the brunt in the front (cause that's where he was) and a ranged caster is picking on the cleric. On my turn I CaGI & AP Divine Power - end result is cleric + rogue are no longer threatened, between pull and push, and all the minions on my side are dead. I then keep 3 guys occupied, with me and the rogue killing one per round, while the swordmage holds off the other half of the combat til we get over there.
The design intent of 4E encounters was to challenge the entire party, not just the defender. Larger areas, few narrow corridors, the ability to move diagonally as quickly as horizontal or vertical. I don't doubt that what you say happened in your game, but it is very far from typical and should not be used to debate that the potential AC delta is reasonable.
It should be used just as much as a hypothetical 'The range 20 character gets attacked against AC every encounter' should be used

I mean, I've done combats in which AC doesn't get attacked _at all_, nevermind had ranged characters going after AC. Those are actually pretty rare in Paragon - mostly going against FRW.