Yes, in some ways it is. Sumi-Otoshi and Tai-Otoshi are both hand throws, both rely heavily on breaking balance primarily with movement, and both throw by placing uke’s weight over a corner.

With Tai-Otoshi you also use your leg to block movement, and the direction of the throw is to the front cover rather than back corner

Breaking your partner’s balance is the first step of any judo throw, and is known in Japanese as Kuzushi.

It is much, much, MUCH easier to throw someone who is off-balance; so this should be your first goal of any technique, but how do you do it?

There are various ways to break someone’s balance to throw them. You can push or pull your partner to the point of being off balance in the direction you want to throw them.

Or, you can use a set-up technique. Attack, with the intention not to throw, but to break balance. For example a good kouchi-gari will make uke stumble backwards. At this point they are off balance and you can follow up with a second attack like ouchi-gari or osoto-gari.