Traders, please share your experience with backtesting tools - what feature(s), improvements you wish they had

Hey everyone, me and my friend are exploring the idea of building a backtesting platform focused on Indian markets from actual traders before writing we started working on the idea. For those who've used tools like Algotest, Stockmock, etc, tell us what’s worked for you, the features related to backtesting that you were thankful it had, your experience with these platforms and also what's frustrated you the most? It could be data quality, speed, the UI, limited strategy types, or something else entirely. Tell us what’s a feature you wish existed but haven't found anywhere? Feature(s) you would have loved to see, and made you go “I would have paid for it if they had it on their website”. Also curious to hear from anyone working at or with hedge funds or prop desks - do you backtest internally or use a vendor platform? What gaps do you see between institutional-grade tools and what's available to retail traders? Any insight helps, thanks in advance. We are a bit in the dark about how enterprise/professional traders go about testing their strategies, so insights on that would be greatly appreciated.