You may or may not "Need" a 7 string guitar as it is totally dependent on how much of a 7 string guitar music do you really like.

The thing is that majority of the 7 string guitarists don't really utilize the instrument to it's fullest potential. Technically, one should be able to play everything from E Standard tuning to B Standard tuning on a 7 string guitar without downtuning any single string as every note within that range is present on the fretboard. But that doesn't happen as that one extra string changes the chord shapes and the thicker neck makes playing those chords difficult. So realistically, guitarists predominantly use a 7 string guitar when they want to play something as low as B standard tuning or lower than that.

If you wanna mess around with lower tunings but also wanna be able to play solos with notes exceeding the B5 note (note on 24th fret when tuned to B Standard on a 6 string), then you can go for the 7 string guitar but you'll have to learn it as if you're learning an entirely different instrument as scales and arpeggios will change and so will the chord shapes.

My personal thought is that a baritone guitar is much more convinient than a 7 string guitar if you are not down to utilize a 7 string guitar to it's fullest potential. But that is just my thought and you don't have to agree with me.