Got a used 2011 Cube - now thinking it is sluggish on takeoff

My GF got a 2011 CVT cube with 68K miles from a woman who is moving across the ocean (ie, probably not a fraudster or flipper dumping a cube with a known bad CVT).

The test drive went fine, but now I'm thinking it is sluggish.

What concerns me is the frequent slowness of taking off in an intersection. I need to floor it, and I can count to 4 or 5 seconds before finishing the turn.

When I floor it, I don't think the engine goes to high RPM, which would seem to argue against slippage. But I don't understand the feedbacks that happen inside the transmission and its control mechanisms, so I don't if the engine should rev high if CVT is slipping.

It also doesn't seem like this happens all the time, but it might vary. It might also be a function of how long it has been driving (hot oil?). My impression is that initial takeoff is better.

Check engine (fault) light is off, but flashes on startup as it should. Could an OBD2 tool still show something?

I understand that CVTs are rubber-bandy, but I don't have a good feel what is normal for a Cube CVT. How bad is it to be able to count to four seconds making a turn? I'm more used to the rigid response of a manual transmission where you can burn rubber if you accelerate hard in first.

Is there a chance that fresh transmission oil would perk it up? I would change it myself with OEM Nissan NS2. Do I need to take the pan off and swap the filter, or is a simple drain and replace enough? My impression from repair manual and youtube videos is that it takes 7 quarts with pan removal and about 4.5 with just a drain and replace.

I read a old reddit thread where a Cube's sluggishness was traced to a bad brake sensor - it thought the brake was pressed, so reduced power. Does anyone know how to check if this is the case? The brake light doesn't seem to be on, but it could be a different sensor.