The best way you're likely to make money is at the very beginning - via the welcome bonuses that are used to entice new gamblers in. They can often be quite generous, as they are a one-off designed to build repetitive habits to bring a player back, but you need to be very careful while reading the terms. If you can deposit a small amount to unlock a big starting bonus with minimal strings attached, then cash out after the requirements are met and withdraw your free money as soon as you can. That's possibly the only way you're going to win against these predefined odds.
Yeah, couldn't agree more. It's all about the house edge at the end of the day, everything else is just too difficult to calculate.
I don't really like those deposit bonuses though, the wagering requirements make it highly unlikely you'd ever end up with anything left... a 40x requirement (the standard) wipes out at 2.5% house edge, but since slots are usually what you can play for the requirements, RTPs wipe them out quicker.
Think the only way to visible maximise profits if sports. Odds are clearly weighed, juice is immediately apparent. Bet where the odds are best, frequently, and taking advantage of boosts and price promos. You may not come out on to anyway if you bet unlucky, but when you do win, you don't leave money on the table.