Well I wouldn't be able to complete an entire section of Tartarus in one night on Hard so I'd probably be much higher, really the trick is just mess around with fusions until you get a persona that dominates the boss
You'll end up dying a lot randomly to bosses. Quite a few bosses have the potential to kill you in one turn if RNG decides they'll all target you with their strongest/most effective move. In general they have better attacks/resistances that what you carry around.
If you are playing blind, that means you also don't know what the boss's element is or what attacks it uses, so it's harder to prepare. This is worse in early game because there are fewer personas in general with null elements/resistances you really need, and the lower persona carrying count makes it pretty much impossible to go into a boss fight ready for any situation. Several times I would get wiped and then come back prepared and destroy them, either because of my preparation or I just got luckier with the enemy's moves.
Ex: There's this trio of bosses (I think someone said they're like hulk hogans) that use revolution, power charge, and spam physical attacks and destroy you. First playthrough in FES I recall I pretty much died turn 2-3. Second attempt I think I managed to tank them with a higher level persona that resists phys, in addition to spamming their weakness so they couldn't hit me (I didn't live long enough first attempt to figure out they had a weakness). In P3P I destroyed them in a couple turns due to being overlevelled and knowing their weakness and what they used.
This happened again when I encountered a trio of bosses (I think some knights) that use mind charge maziodynes on me, with elec break on the side. I brought Yukari (and maybe Aigis too?) and the enemy got one more and I was almost dead by end of second turn, only saved by my Akihiko who got Elec breaked and tanked a hit for me. I didn't survive third turn. The next attempt I didn't bring Yukari and brought Ken as a healer instead, and I had a Persona with absorb elec, and it was a lot easier.
tl;dr random bosses will occasionally destroy you first time through. And sometimes you can happen to have a good team and destroy them first try, though sometimes it takes a second+ attempt.
Also despite the fact I posted that pic with Sho, I didn't really understand it that much myself, just found it mildly amusing.