“There’s a reason why people always play in the same tunings” - that’s some dumb shit right there. You play in the same keys/registers but I don’t need to use a 4 string bass in drop D when I have a 5 string in B standard where I can play the same stuff.

Another reason he has no clue what he’s talking about - the string gauge/tuning for his super low E is going to have a similar timbre and thickness to your G string, your normal E string will be thicker and have heavy timbre. Using the 5th fret E on your B string will give you even more thickness on it. You don’t need to change anything.

You might want to keep your options open if he persists. Some people are just really uninformed and will just make shit up and spread myths/mistruths, I see it all the time with gear related stuff.