At $300/mo, your total cost would be $18K for 3 years after sales tax and all fees other than registration.
Purchasing with Tesla's 6.7% financing and qualifying for the $7500 tax credit would cost $38K for 3 years.
So by committing to a lease, you're betting that the car will depreciate by much more than $20K - enough so to make all the commitment, effort, and hassle of a lease worthwhile. So what price do you place on sanity and freedom? If, for example, you'd be willing to give it all up to save $5000, you'd effectively be betting that a 3SR will depreciate by more than $25K over 3 years.
That kind of depreciation hasn't happened to the Model 3, unless you extrapolate the recent Covid-induced bubble - which clearly does not apply to today's very normal pricing. The 3SR+ sold for $38K throughout late 2020 and today they're consistently listing at $30K on AutoTrader with 30K miles. So, about $11K in depreciation if you include taxes and fees.