Almost every encounter(6/8) there had saving throws involved with critters with special attacks. Saves are one of the things where 5E kind of struggles with due to saves not scaling its a weak point of every party in 5E for the most part.
Mate, youre a party of 5 x 9th level PCs. Most encounters at this level will feature stuff hurling out saving throws of some kind.
Perhaps if you took resilient instead of GWM...
You are also taking full advantage of stupid rules with low CR critters as 5E stuff has lots of hit points. 3.5 also had a similar rule.
Im not taking 'advantage' of anything mate. I couldnt have used a broader range of encounters if I tried. In one adventuring day you deal with undead, humanoids, giants, fiends, a dragon, aberrations and constructs. There is a solo encounter, a mob encounter, and a few featuring low CR Mooks.
You may not be using spellcasters but every encounter has some sort of AoE in it and a pair of flames skulls which I referenced as being an abuse earlier. Getting hit with multiple fireballs can suck in 5E and 2 flameskulls can drop 32d6 damage. The flameskull in LMoP is a pain and I have used a pair of them to almost TPK a party when combined with other monsters.
The Orcs dont have any AOE's (and are vulnerable to them) neither do the hook horrors. The dragon and the illithid have only line attacks (L bolt and breath weapon). The giant encounter has the one AOE (a winter wolfs breath weapon).
Only the flameskulls have fireball (5th level, 1 each) and the Mezzoloths have cloudkill (1 each).
In a party with 20 healing potions, 2 paladins, 2 clerics, the healer feat, and 40 HD of healing from short rests, I think you'll be fine.
A spellcasting Dragon a spellcasting Illithid, 7 critters with paralyzing attacks+ demons, 16 Orcs ignoring the encounter multipliers for low CR critters. I'm trying to work out why a few of those critters would even associate with each other. Orcs having a pet Wyvern maybe.
You dont have to work it out mate. Im the DM. I know the reasons they're there already.
If you're curious the Orc chief rides the Wyvern and the Orcs are the guardians of the tower (hired goons). The dragon and the illithid parties are the emissaries you need to slay. The encounters with the [Mezzoloths and undead] and the [Flamekulls and Horrors] are trap rooms [for fluff, the flameskulls are the flaming skull heads of the Helmed horrors that fly off to attack the party]. The Giant is the captain of the guard (with a grudge against the dragon) and the Hooked horrors are thralls of the Illithids brought up for extra muscle should things go south.
Not sure why a 9th level party with 2 clerics and 2 paladins are worried about half a dozen ghouls by the way...
Your biggest issue is getting through encounters 1-6 with enough juice in the tank to fight that Dragon (particularly after fighting the Illithid caster and his thralls). Thats the cheallenge here - a dramatic race against the clock to take down two nasty little encounters.
Every expenditure of a resource (spell slot, action surge, smite etc) is a meaningful choice and not an automatic go-to.
I have used a few tricks like that myself just not generally all at once. I can't think of to many 5E adventures with encounters like that either.
Dude, there are no tricks here. I literally used a mix of encounters of different types and sizes and compositions, relying on the 6-8 [medium to hard] encounter/ 2 short rest paradigm.
Its fair to say that your party would be challenged in this adventure, and GWM and SS wouldnt dominate yeah?