That is one interpretation. It is not consistent with other spells of this type, however.
Every other spell that summons a controlled creature is very explicit about how control works. They lay out in detail whether you need to take actions to give orders, when the summoned creature acts, what it does if not commanded, etc.
Find greater steed just says "you control the mount in combat." If read the way you read it, that leaves a host of questions open about how it's supposed to work. However, if read as a reference to the mounted combat rules, it provides the same level of precise detail as all the other summoning spells.
I might base its behavior off the PC's paladin oath.
I always get upset when a DM suggests that a player is getting too powerful with a perfectly logical, legal combination of abilities.
I always get upset when a DM suggests that a player is getting too powerful with a perfectly logical, legal combination of abilities. No. They are not too powerful. They are simply ready for more than you are giving them. I threw the freaking Demogorgan at my players at one point because I knew they were powerful. Up the anti. Make your monsters fight better. Rejoice that they have figured out something powerful, because now you can bring about something even more so. Let them shine, and then knock them down. If it becomes that big of a deal, have the baddies target the steed. Make a baddie who curses the steed so it becomes sickly and unusable, and force them on a quest to heal it.
That's just indicative of how poorly designed it is. At low level a beastmaster who chooses an animal as his companion is typically worse off than the exact same character ignoring their class ability and simply buying the same trained animal.It just seems like this one single spell makes any character who takes it into a better version of the beastmaster ranger. I know the beastmaster is universally considered to be poorly designed, but it doesn't seem like one spell should be able to outdo an entire class.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.