"I have always had doubts about whether the RAF would be right for me" - if there is doubt, there is no doubt. Joining the military is a huge undertaking and in my opinion is more a lifestyle than a job or career.
"...be involved in this forced group bonding, even if you would want to cultivate friendships with just a few people. This is probably not the right attitude for the military, so I wouldn't get very far." I disagree in that it isn't 'forced group bonding' and that you could succeed in the RAF while disassociating yourself from all but 'just a few people' however, it is unlikely that you will fit in. The RAF is about camaraderie, making best friends with people you've only just met and being friends when you bump into them again years later. You are likely to be viewed as an outsider, and not because you don't want to get boozed in the bar.
"Second, the bases are depressing, isolated and you could end up working in unfavourable parts of the country." yip, they might even be in unfavourable parts of the world; I've spent over 2 years in **** deserts around the world living in portacabins and tents, half of that time in non-flying jobs. But it is the camaraderie that makes it doable and I've seen and done some interesting stuff.
"wouldn't you rather work in a pleasant town/city" yes, there are a number of places I would rather work in however, the military isn't a career where you get to choose. If you don't want the risk of being posted to deepest darkest Scotland to fly Typhoon/P8, again, the RAF is not for you. If you want to make some great friends and make the most of whatever crap mess/quarter you get posted to then come on board!
"I know people who are on 1+ year holds between IOT and EFT. It could take over 5 years to become operational." Holds are an unfortunate norm for RAF flying training. You might get lucky; I was relatively lucky and only held for 1 year in total. With re-streaming it took me 6 years to get operational. The way MFTS is going, my guess is there is a good chance you hold longer.
"Even then, you might only fly 15-20 hours a month." You might not fly at all some months. You might bounce from one currency to the next and only get good continuity when you go on operations. You might get posted out of area to a Flight Safety job and not flight at all for 6 months; worse, you might get posted to one in the UK and not fly for a couple of years! Some people get lucky and only fly, but the old adage that you are officer first, pilot second is probably pretty accurate; I have only 2000 hours after 15 years. In saying that I have really enjoyed the variety and challenge of the stuff I have done when not flying and as a result, don't at this stage have any designs on leaving.
"Could I also ask if any of the flying ever gets mundane" yes, I know guys flying on operations right now who find the flying boring. It's all relative though, as it is still more interesting than flying airliners. And even boring flying is more interesting than a lot of desk jobs!
In short, if want to you choose where you live and mainly just fly multi engine aircraft with people you don't know and don't have to socialise with, go to the airlines. If you want a career with variety and some great friends, join the RAF and give it 100%. But if there are doubts, there is no doubt.