I would like start by pointing out that you can do tax loss harvesting (TLH) at Vanguard. It's not a unique feature of robo-investors.
Back to your original question, if you were to dump 50K into an account (I'm assuming this is all money not in a tax-advantaged account such as a 401K or IRA. You can't benefit from TLH in a retirement account), you may outperform the fees associated with the robot investor.
But I would be cautious of this assessment because the value of TLH relative to the fee diminishes as your account grows. Over time, as your stock/find/ETF grows in value it becomes more unlikely for you to be able to TLH that particular share. EG, if you bought a share of VTSAX ten years ago and its value has since doubled, you would need that mutual fund to drop in value by half before you could consider TLH that share. So since the market in general goes up over long periods of time, you can usually only take advantage of TLH with recent purchases.
With that in mind, your robo-advisor fee is a fee of your ENTIRE account, including shares you bought 20 years ago that you likely can't TLH. So to keep up it would have to do a better and better job at TLH your recent purchases.
Personally, I do not believe TLH alone is a reason to get a robot investor. It's not that difficult to begin with if you DIY, maybe taking a few minutes of work each year to do.