Biggest drawback of pre-seed company is that they are constantly pivoting. There is actually a term for this, it is called pivot hell.
Every time they pivot, they will be 100% convinced that this particular idea will work, and they will convince you to put weekends, late nights into building it. Of course you will be promised that you will get a balanced life once the product stabilise.
But, they will pivot again, and the story repeats.
At any given point of time, no body remembers the effort you have put into building products that have been discarded. Gratitude for your hard work gets reset to zero every time a new idea comes.
You will have teammates acting as cofounder, some of them might literally be sleeping with founders or their close ones. They will add a few extra dimension to office politics.
In Large orgs, people get into politics so that they grow in their career, even if it happens at the cost of others. In small startups, there are a few extra dimensions. Founders play manipulation game to make you work harder than you should. There are higher chances of growth, so politics is generally more intense. Founders generally have their favourites, and these are the only people that gets rewarded, but you will have to spend 2-3 years to know who their favourites are. Why it takes 2-3 years? They have to make everyone feel special and favourite so that they can extract as much as they can from you. They might have started giving you a vibe that you special for them, generally this process starts from the interview process itself.
Salary increments may not happen. Next year, they may come up with some stories to make you feel guilty for even thinking about increments in times that are tough for company.
The boundary between colleagues are friends are more blurred in small startups. It is so friendly that they will call you as a friend when you are on sick leave. But, become a colleague and assign some task in the same call itself.