How can a BBEG deal with a Wall of Force and Sickening Radiance spell combo without trivializing it?

This question has already been asked in general form here, but was closed as too broad: "How to deal with broken combos?". I’m going to make an effort to make the scenario I’m asking about more specific to keep my question open.

The spell sickening radiance (XGtE, p. 164), cast just before a wall of force (through a readied action or something similar) can trap and kill many solo Big Bad Evil Guys (BBEGs), with just two casters. This combo is particularly lethal because of the levels of exhaustion the spell gives, but could work even with other persistent damage spells. Sickening radiance is a spell that creates a persistent area of effect for 10 minutes that deals radiant damage and gives exhaustion on failed saves.

The combo works like this: wall of force (WoF) caster readies their action, with the trigger "cast WoF on the BBEG when my friend casts sickening radiance (SR)". SR caster’s turn comes, and they cast SR, centered on the BBEG. WoF gets cast on the BBEG as a sphere, trapping the BBEG within the wall of force for 10 minutes while they get exhausted to death.

What actions can I, as a DM, take to make a fight with a BBEG not as trivial, while still rewarding the two spellcasters’ ingenuity?

I classify "rewarding the two spellcasters’ ingenuity" as at least forcing the BBEG to spend a limited resource to deal with the problem. So a BBEG having disintegrate is one option for what I can do, but giving the BBEG a teleport as an action (or legendary action) is not.

How do I prevent a homebrew Grappling Hook feature from trivializing Tomb of Annihilation?

I am currently running Tomb of Annihilation and letting one of my players play a Revised Artificer homebrew.

One of the features under the Gadgetsmith subclass is a Grappling Hook, with this mechanic:

As an attack or as an action, you may target a surface, object or creature within 20 feet. If the target is Small or Smaller, you can make a Grapple check to pull it to you and Grapple it. Alternatively, if the target is Medium or larger, you can choose to be pulled to it, however, this does not grapple it.

Initially, this is no big deal as the character has weak HP scaling (D8), so it was fine for the player to grapple himself around the battlemap to safety. He then, however, got this upgrade:

Enhanced Grappling Hook:

You enhance your grappling hook, increasing its range to 40 feet. Additionally, the enhanced power of the grappling hook means that when pulling yourself to a larger or larger creature or object, you can drag one medium or smaller willing or grappled creature within 5 feet of you with you.

Emphasis mine. That one clause is beginning to cause a headache for me, as it is a resource free, instant Misty Step + 1 ally to any object within 40ft.

I am certain this will break many obstacles in the actual Tomb. To give a few examples:

I think you get what I’m saying at this point. The hook+1 mechanic is broken when it comes to dealing with a significant portion of the Tomb’s obstacles.

There is the option to nerf it entirely and render it unusable in the Tomb; the dungeon does have powerful, world-altering enchantments upon it, so it would not be too out of the box. I am hesitant to do this, however, since the player greatly enjoys grappling around and being mobile.

Overall, my key grievances with this mechanic are this:

  • The Grappling Hook is free. It requires no resource usage to transport himself and a companion within 40ft. Compare this to Fly, which also negates a lot of aspects of the Tomb, but is a resource that is used as the player just ferries everyone across/over obstacles.
  • There is no check involved. He can bring any willing companion without fail. However, if I were to involve an Athletics check, his character would almost always fail abysmally.
  • It is core to his kit. If I were to take it away, it would crush the player, and I have already allowed it far too long to remove it entirely.

Is there a creative solution/compromise I can bring to this player so that I can make the Tomb experience more gripping and exciting? Or am I blowing out of proportion how good his grappling hook ability is in respect to this adventure?

Answers that cite prior experience with either this module or this/a similar mechanic would be greatly appreciated.