The players in my Rhunaria campaign know well enough that there are bigger fish. The first adventure took place in a city founded by an ex-adventurer, who had some impressive feats to his name, though nothing close to 'epic'-ness or whatnot.
Early in the second adventure, the PCs met another group of adventurers in the tavern, sitting around a map and discussing strategies for assaulting the trap-and-monster-laden castle appropriated by a crazy wizard some time ago, one they had tried to bust into before but failed. These adventurers had some expensive-looking gear and the warriors bore many scars, though the PCs couldn't tell just how powerful they were, they did SEEM like they must've been at least a few times more experienced as the PCs were as adventurers.
The party's seen a high priest destroy a minor evil artifact, and have met an old human wizard in a hobgoblin-founded city, who owned a modestly small tower (with a normal small house-like addition on the side) and was recommended by folks in town as magic items dealer and identifier, as well as an alchemist and magic item crafter, though he did only infrequent business as such. He seemed a little unhinged to the PCs, but he was nice enough. They did get a very ominous feeling from the tightly-sealed, be-sigiled, thick iron door to an iron-lined room in his basement though.... What made it obvious enough to the PCs though that he was fairly powerful was the tiny runes lining the inner edge of his doorway, and the incinerated corpse of a burglar lying at the threshold in the evening, when the PCs realized they had left the door open after following the wizard inside to talk business. Little more than ashes and shards of bone remained of the poor berk, making it obvious the wizard had a fairly strong magic trap or ward of some sort around his door. And to the PC mages, the wizard's study looked like it had some fairly powerful books. Plus the numerous powerful magic auras their Detect Magic cantrips revealed on most books and trinkets and relics on the study's shelves, while the wizard was fetching them some tea.
The PCs have fought a pair of mid-level kobold mages, each controlling a Bronze Serpent and hurling fireballs, ice storms, and lightning bolts..... The PCs have traveled briefly with a dwarven fighter overly obsessed with hygiene and appearance, him and his warpony decked out in rune-etched mithral armor and carrying an obviously-magical axe, hewing through the same kinds of foes that were giving the PCs a run for their money. The PCs took great delight in harassing that dwarf and pulling pranks on him......he was a jerk, he was.....though one PC bard pushed him too far with some thievery, at which point the dwarf beat him within an inch of his life with a few bare-knuckle punches, which made his point. The PCs did get to see him get battered around and challenged though, like against the Bronze Serpents. He never took the spotlight, but he did give them something to compete with, and a great NPC they loved to hate until he finally left the caravan, when it reached the destination.
They've traveled with a Rizan priest-diplomat who, even though having begun his priestly training as a monk, was a powerful enough cleric to invoke a few Flame Strikes in a single day, and call a Lesser Planar Ally at one point. They've met a few powerful dwarven mages from the Sterling Golemist Arcanaeum who helped them out briefly and sold them some magic items, including one who performed several Teleports in a row, effectively shuttling the large group of PCs a few at a time between the Arcanaeum's guildhall to the middle of a forest past at least one mountain range and at least one valley. The PCs have met with a great wyrm gold dragon who brought them to his lair for a chat, until he grew bored with them and their minor insults (some were rude, others just clueless, and the rest just tried to cover for their foolish comrades), sending them away. He had giants and golems for guards and servants, and an experienced-looking lizardman fighter decked out in rune-covered adamantine gear.
They've basically had enough run-ins and meetings of powerful individuals (compared to them anyway; most of the potent NPCs they encountered were in the low teens or slightly lower in level than that) to know that they aren't all that mighty and invincible, but at the same time, they've noticed their growth and know that they're much stronger than they once were, and may yet become as powerful or moreso than the people they've met along the way. None of the powerful NPCs took the spotlight, and there was never more than 1 or 2 around at a time (and plenty of times when there were none around); most of them the PCs just met with briefly in one or two sessions. But the players did have a good enough idea that they couldn't really just fly off the handle, while knowing that at least most of the powerful NPCs they encountered were pretty well each staying in one place and keeping busy with their own concerns, so the PCs were often the real people of action on the road and wherever they went.