The answer to your question is no. They are not novaing. They are using certain feat, power, and class combinations that are enormously effective over a nearly indefinite period.
Most such combinations are resource dependent. Ergo hit them with more encounters. Drain those resources.
You claim to be a good DM; are you suggesting that you cant design [CR/ XP budget] appropriate encounters for your own groups PCs?
I've pointed these combinations out, but you don't believe me. I cannot force you to believe something you don't want to believe. All this stuff is coming not just from me, but from multiple sources using the exact same combinations that are highly useful in a huge variety of situations. The bless and aura of protection combination is useful against anything with a saving throw. We point this out and are told it isn't a problem. Aura of Protection is always up. Bless is a 1st level spell castable by multiple classes. It's enormously easy to keep up for every encounter even if you have to recast it a few times. There are mutliple effects like this.
Bless isnt an issue. Its a nifty spell that adds +2.5 to attack rolls and saves for the party while it's active - for the price of your concentration slot (so no walls of force, spirit guardians, polymorph etc). Great buff, but not a game breaker by any stretch of the imagination.
I don't understand why you can't admit there are quite a few power combinations in 5E that are easy to obtain and hard for a DM to counteract adventure after adventure after adventure.
Im not saying that they arent hard for a DM to counteract. DnD has always gotten harder to DM appropriately at higher levels. Clairvoyance, teleport, high level divination effects, power combo synergies etc are (and always pretty much have been) a thing. The higher the PCs level, the more skill you need as a DM to do it.
As a low level DM you can throw a bunch of orcs in a few rooms, throw some goblins in a few more, an Ogre here, a gelatanous cube there, maybe whack in some ghouls and 'presto' youre done. As your party advances in level, you need to be more creative and put more thought into what youre doing - your players options increase, so does your DMing ability need to be on song.
Watch what happens when an inexperienced DM throws a one shot high level adventure for experienced players. He designs a tower with the BBEG on the top floor, and designs 7 levels of devious traps and monsters - only for the PCs to use divination magic, teleport in invisibly, and turn the tower foundations to mud with stone to earth, or ethereally bypass the lower levels and head straight to the BBEG, or teleport/ fly to the top and raze the BBEG from surprise. Thats not bad players (quite the opposite) - thats bad DMing - the DM did not know his players capabilities and failed to design the encounter to challenge them.
It takes a good DM to challenge higher level PCs. Its an art form, not a science. And you dont do it by ratcheting up the difficulty of encounters - you do it by playing to your parties weaknesses and negating your partes strengths (not always though - let them shine from time to time).
Again, I could take the PC's you provided for this experiment and design a chain of 6-8 medium-hard encounters specifically for them that I guarantee you would challenge them despite 'optimised choices and tactics'. I would DM it accordingly too - not many players would be harping on about 'optimised options' at my table, becuase they know its pointless; 'anything you can do, the DM can do better' is my mantra. Play your character and have fun.
TL; DR - Dont be a lazy DM. Know your players and their characters. If theyre always metagaming, mix up your monster capabilities and challenge those expectations. If theyre always using fixed tactics, design your encounters so those tactics are unavailable to them, or even are the worst option and not the best. If theyre nova-ing, force more encounters on them via the environment. Give them the odd encounter where their tactics work. Mix it up.
You do it properly and your Players are always on their toes, always guessing and much more enganged with the game.