From personal experience I can beat all level 3 raids with 3 people but can’t beat any level 4 raids with everyone I know who plays Pokemon go - a group of 6, we even got eight for Tyranitar and failed. We weren’t the highest combined level to be fair. The legendaries were the most annoying. I got zapdos, moltres and entei, I lost to an articuno when our big group did maybe about 10% of its health in time. I was in A group that beat lugia but couldn’t catch it. It was after these irritating experiences (I also had a perfect IV entei run away from my 2nd account) I decided to stop doing the legendary raids. I stuck to my level 3 raids and powered up my zapdos all the way. So I was thinking of a balancing move by Niantic to stop the annoyances in the battle system from being as bad. It’s a pretty simple move and I think they should lower the raid cp for less people but keep it high for the groups. They could make it that if you went up against a legendary on your own you had a chance at getting it just like in the main games. It means that people like me could see a legendary raid on the nearby and get excited rather than disappointed because I can’t use that gym for battles/berries for 2 hours. The alternative (I would almost prefer this a bit) is they start a quest system for the legendaries or offer them in eggs etc. This wouldn’t only be for legendaries though. People who live in areas without enough people to do even level 4 raids would benefit hugely. As for players without a gym in their town, they really need to look into getting a gym and pokestops submission system inside pogo itself.
EDIT: Just for clarification I went to a city on a trip and got my first legendaries there. Entei was later on in the city again.
EDIT 2: I realise now that the 2 hours thing is wrong - it’s 45 mins.