1: any airdrop that "have no end" they often runs for 2/3 months, majority are not true. real airdrops don't last more than a month.
Depends on location of airdrop. If an airdrop is hosted on a third-party website such as Coinmarketcap, Coingecko, etc. it should have a period. However, if airdrop is hosted by a project website itself, it can last as long as they want.
2: 95% of airdrop given to "all participants" is not real. Normal airdrop is mainly for a limited number for top referrals.
You misunderstood between airdrop and referral bonus. Some airdrop campaigns can be distributed to random addresses or top holders of that project or of partner project. Possibly top referrers if they want but I have never known about it.
3: Any airdrop promising you high amount of their token equivalent $5000, $10,000 or even more without through referral bonus may not be real. Real airdrops don't give such amount, unless you are claiming on their site where you pay gas fee,
Sounds correct.
However you should know that sometimes they just try to play with words and want to create hooks for their airdrop campaigns.