I know a lot of what has been discussed in this thread overlaps discussions in other threads.
However, I do believe that given the size of our Army and our budget, especially moving forwards Post-COVID, we should decide what kind of force we could excel at being, and focusing on absolutely excelling at it.
Could we do one light, one medium, and one heavy brigade with a decent reorganization? Absolutely. It wouldn't even cost much money to be honest, with the exception of some enablers that need to come down the pipe anyway. (ATGMs, AD, etc.)
But, lacking the aggressive transformational mindset of the USMC or Royal Marines, and not preparing for a specific conflict - I think we should focus on being top notch in 'light' or 'medium' operations, with what we have.
The HAPC asset may be extremely useful in some situations, but we need to ask ourselves the questions asked previously. Would they be used often enough to justify the cost? How could we deploy them since they can't really be transported via air or rail? Is it a capability that is required in the near future? etc etc