no. and here are some valid arguments as well as helpful suggestions,
Pantheon is fine, his shield is only activated every 4 attacks or if he uses Aegis of Zeonia. and even then, it only blocks 1 attack that deals more than like 40 damage. So, it CAN be countered if you can work around that( i.e. not playing someone like gangplank). Mages work very well against him and he doesn't bring very much to the table late-game in terms of teamfights.
Mordekaiser is always going to be a valid pain in the ass, I wholeheartedly agree with you. BUT, his shield has a very fast decay nowadays and can only be replenished with the damage dealt by his spells, how do you stop that? thats right, SILENCE. Silence and a good amount of either burst down to zone him out or dps to hold him off. Unfortunately, I cant think of any champion off the top of my head who has silence and dps BUT leblanc is quick and has a tremendous amount of burst damage to give you the advantage early game. so, try giving that a shot.
Singed has alot of sustainability and is known as one of the toughest tanks in the game. but currently his base stats at lvl 1 are 18 armor with a 3.5 per lvl. more than average but manage-able, pick up some armor pen. and some poke and you should be just fine. and above all else, remember the rule of thumb: DON'T. CHASE. SINGED.