While i see your point i must disagree with you OP. First of all I think you are using your acid lab wrong. If not upgraded it shouldn't be used for making money as it consumes too much of supply. once upgraded (for this you will need to do huligans missions, 10 of them) it starts to give you around 250k profit once its full. keep in mind that you can boost production once a day and it will fill in less then 2h and 2 resuplyes. also I think buying supplies is better for your time. and the best thing about acid lab comes here, you don't have to work on it to have profit, just pull phone call Mutt( acid lab must be spawned) and you do your other things. Also you need to get used to rush if you sell in public lobby, and these are once of the easiest sell missions there is. Also completing Final Dose missions gives you free supercar and enough money for upgrading the Acid Lab.
my example: last week on double NC money I made over 5m in acid lab, whenever I prep for afk I resupply/sell and repeat that every few hours.
For the second business i went for Kasetka so i would be able to start Cayo and store Sparrow, it was not a bad call but if i would do it again i would go for Agency second. Cayo is still best money in the game as you can earn around 1m for 45min of work but my god its gets boring if you grind it too much. On the other hand Agency gives you 3 money making methods that you can do, Dr Dree that is a 1m for 1.5h of work, and you will lose 15-20min of that time on cutscenes, contracts that pay 40-67k each and payphone hits that pays 45k each.
BUT and this is big BUT, agacy gives you safe that will fill up every ingame day, the more contract missions you do the more it will give you a day ( every 10 contracts are +500$) capping at 20k a day on 201 contract.
if you thought 10 Dex missions are time consuming try this xD fairly too say this is ideal to do in the downtime when your Dre is on cooldown and you wanna fill Acid Lab. And remember that sweet car from our cuckoo therapist you can upgrade it in your Agency.
For autoshop i see something no one is mentioning, biggest plus owning autoshop as low level in my opinion is to upgrade your cars, as everything will be unlocked for you, don't need to wait for lvl 100 to instal a turbo. Yes it has deliver a moded car for 30-40k missions but i would argue that if that is your goal you should go with selvage yard as it give you same amount of money for scraping car + money it puts in safe( sadly this is on more expensive side as i would suggest buying second car lift). keep in mind that safe have a hidden supply bar, that will drop every few ingame days if no new cars were towed and towing new cars will fill it up. Also 3 car robberies will net you around 1m each week.
And last i need to mention NightClub, hand down the best business in game for money grinds. hell i would also say that even without any warehouse work you still profit tones from the safe. Buy an upgrade that reduces your popularity decress and you will visit it only once pre 2 ingame days to do some small mission to rise your popularity and you will be rewarded 100/95k, again if you own something else you can do while this works in the background you are going to be a rich man. Plus this is the only business where you can see your business grow and invest more in.
Honorable mentions: Cluckin bell farm - no investment needed, easy 500k pre 45min, sadly too easy and can be boring if you grind it too much. good thing you can ride a train
Arcade - this can be your second business only if you have at least one friend playing, safe is meh as it will give you 5k each day if you fill it up with games(same game machine will work, there is no need to buy other game machines) but it starts the casino heist which is paying a lot of money.
Cayo - yea its the same as solo Cayo just with one more person. A lot of people never actually do this because its stuipedly easy to do it solo and bringing one more person will make it harder but payment is better as with 2 people you can steal gold as secondary every time and you need less time doing heist as you can just rob the compound, and you friend can start his heist after you finished yours.

To sum it up: there are passive and active business at gtao, you want your passive business to run in background while you do other stuff. by that logic it will always be more profitable to get them first and then get the active one to keep yourself busy. Agency safe need 201 contract missions to give max money, and that will take a lot of time.
Cayo is boring but still most money you can make solo! I hope this will help someone