I’m a layman but from what I’ve read recently, 92 to 78 is 14 degrees; the typical temperature differential is a maximum of about 20. There may be a few more degrees you can eke out, but you are getting a majority of the potential benefits
Has it been working alright throughout the rest of the season? I had an HVAC system that was incorrectly wired by the installers, so it actually ran the AC and heat pump at the same time, cancelling each other out. Might not be your situation but you never know!
You can’t “run the heat pump and a/c at the same time” because it’s a single unit. There’s a valve that slides when powered to switch the hot side with the cold side. That’s literally the only difference between a/c and a heat pump.
That could be part of a problem if it isn’t circulating.
Make sure all the vents are open and not blocked by something inside. Switch filters if you haven’t recently, and make sure they are the right kind for your unit. If you can get to your duct work, see if it is leaking anywhere as that will reduce the pressure at the vents.
If you have ceiling fans, turn them on to help out. If you aren’t already, close curtains to block direct sunlight (east side in the morning, west in the evening).
I would recommend having a different company check it out since they won’t be defensive about the prior work.
Could be a refrigerant leak. It will still run but won’t cool.
Have you replaced your filter recently?
Does the unit have a standard 1" thick filter or a thicker one?
1400sqf = 130m2
Typically in Australia we’d size for 180W/m2 which in a domestic setting gives plenty of heads room.
130x180 = 23.4kW unit. This size it would be a ducted unit to ensure proper distribution of cooling throughout.
2.5tonne equates to approximately 8.8kW which only gives you 68W/m2 which as an ex mechanical engineer is completely undersized at least for Australian summer.
Without knowing more the only suggestion I would give is set the target temperature a bit higher. This increases the units efficiency and should help it get to temperature quicker.
If you’re uncomfortable try running an additional fan. The movement of the air will make you feel cooler even if the air temperature is the same.