The books I've read state quite clearly that the current low populations in the Highlands and Islands absolutely are a direct result of the clearances. Sure, there would have been a steady stream of depopulation like the rest of rural Britain, but that is merely a modifier to the surviving population centres rather than the driver of empty landscapes.
Also interesting to follow the second home debate in the H&I compared to Wales, where the Welsh issue strikes me as less acute and significant but far more prominent politically.
Agree with Jon, a big driver of visitor numbers is carbon footprint reduction. As this continues to grow (and the Scottish climate continues to warm) this will only continue. So we need to plan for the future and visitor numbers being much higher still. The viability of remote working is also driving net positive immigration - this will increase too. It is vital people see these areas as they are - currently underpopulated due to forceful eviction and resettlement - rather than nice quiet areas to bottle in aspic for a drive-by peepshow.
Likewise another big driver is the democratisation of information via the internet. When I first went to Barra it was because I'd buy photo books while peers went to travel agents, who sold them flights. Now everybody gets images unbidden direct to their pockets which illustrate how nice Britain is. One extample is viral instas, another is this thread. Covid gave that process a boost but it was well under way before and will continue beyond.
For the OP, I really like Fidden, Barra and Harris. I haven't bouldered much in Scotland but if you like quiet and freedom to roam it's worth noting that long ferry rides are an enduring gatekeeper.