No, the medium tasks are for non-expertise and the hard tasks are for expertise skills. The very hard are expertise skills, but you're yet to identify the reasoning that has a rogue player picking skills for reliable talent under different criteria than the skills he picked for expertise.
Fly expends a resource, one that could have been a fireball. Invisibility doesn't, in fact, beat any stealth checks; it allows stealth checks. Knock also expends a resource and creates a clearly audible knock up to 300' away, hardly a stealthy action.
We aren't really talking about peons, though, are we? In a small town, the targets you hit are merchants, not farmers, and even they can't afford very hard difficulty locks or magical seals very well. Plus, they carry a good deal of coin or goods that are valuable, so it's not pocket change we're really talking about. If you have a small town that your rogue rolls through and robs with impunity and comes up with only a few 100 gold, I'm asking what kind of plague or war is currently raging on the streets.
And, actually, the fact that other level 12 NPC rogues can do it as well exacerbates the problem in the fiction, it doesn't solve or ameliorate it. You now get to come up with reasons they aren't making enough money to live extravagantly knocking over the occasional D&D version of a small bank every other week. You can do this, certainly (and I have), but pretending it's a trivial effort is ridiculous.
I have no idea what you mean by picking skills with reliable talent. last i checked reliable talent applies to any proficient check. Last i checked, expertise applies to up to four of your skill/tool proficiencies whether they came from race, class, background or whatever - so not all of a rogue's proficiencied checks are going to be expertise.
So...
With attribute bonus of 5 and proficiency of +4 at 11th we have the following results:
Moderate/Medium DC15 = automatic with both proficient and expertise.
Hard DC20 = Roll for proficient checks and automatic for expertise checks.
Very hard DC25 = Roll for both proficient checks and expertise checks.
With attribute bonus of +5 and prof bonus +5 at level 13 (same time as 7th level spells unlocked)
lowing results:
Moderate/Medium DC15 = automatic with both proficient and expertise.
Hard DC20 = automatic with both proficient and expertise.
Very Hard DC25 = Roll for proficient checks and automatic for expertise checks.
opposed checks for all cases are against a floating Dc so not as rigid a thing.
As for trivial effort blah blah...
in early DnD editions the idea was not everything had to be shown in a PHB or even books.
But some folks did not think thru.
So you had more than a few games where they had traditional castles as stronghold without magic as high level party objectives and suddenly **OMG** teleport breaks castles etc etc etc.
Rougue or any other 12th level PC decides to go knock over locals for loot, you can choose to handle it as a downtime activity, give them relatively reasonable for their level and time loot **or** you can decide it breaks your game because you put a lot of loot out there with no guards or wards to protect it against foes that would be out to get it. or somewthing in between.
The game rules, the rogue stats, telport, raise dead, open locks, fly, etc etc etc - all those various "not what one might normally see in a non-magic world - stuff do not tell you to in your setting put in "more gold than we are paying for defenses to protect."
if you as Gm cannot build a setting that keeps your characters from breaking your setting, 12th level rogue skill rolls are not going to be on your top ten huge honkin' problems list, IMX. Look at stuff that comes after 12... if lockpicking is your fret point for 12th level.
How about, banks pay for protection wards... so all their locks are "magic locks" and special alarms go off and they have paid some group somewhere to respond when a mage or rogue or other character gets antsy?
Course... if this small town bank has enough gold to make it worth a rogue 12 time AND its basically open season, why hasn't a red dragon flown in, levelled the place and taken the gold? or .... insert any number of bad guys...
But its your game so have fun... i realzied that challenges of type X would become obsolete as campaign progress and the setting de jour, PC objectives and challenges need to address that a decade or so before the "definition of is" was a thing.
As some others have suggested, maybe restart a campaign at 10 if you want those things to be tough.
its up to you