Who decided to be compliant at this stage of the company, you or whoever is in charge of business operations?

> I felt responsibility to make the product as solid and maintainable as possible

Was this responsibility conveyed to you or did you make this decision on your own?

I'm clearly making an assumption here, but this reads like a case where both sides had a misunderstanding about how engineering time is spend. They trusted you with some autonomy to get things off the ground and found out you are making business decisions on your own that don't fit into resource constrained startup operations. There is always a trade-off and corners can be cut, and my advice is to be upfront about the general approach about those and find out how much they are willing to invest in robustness and product quality at a certain stage.