Yes. I think it is quite unpractical, that nearly every country has it's own chess rating system.
Post your OTB, Online and Tactics rating! - Graphs done

Obviously conversion formulas are garbage.
They are, I am still trying to convert USCF of 1050 - according to formula, this is cca. 500 FIDE, which is nonsense. Perhaps I will use uscf rather, or just both.
Did you use this:
USCF = 720 + 0.625*FIDE if FIDE < 2000USCF = -350 + 1.16*FIDE if FIDE >= 2000
I tried that, but I realized that with a rating similar to mine (between 2000-2100) the conversion actually doesn't make sense, because that would make a 2050 USCF have a higher FIDE rating, even though FIDE ratings are generally lower than USCF ratings.
My last chess rating 3 years ago was;
ecf (English Chess Federation) 145
= 1810 FIDE according to ecf conversion formula (145x8+650)
Current blitz rating 1598
Current online rating 1812

USCF - 1800
Blitz - 1720
Standard - 1702
Correspondence - 1989
Tactics - 2153
Let me know when you complete your graph!
Obviously conversion formulas are garbage.
They are, I am still trying to convert USCF of 1050 - according to formula, this is cca. 500 FIDE, which is nonsense. Perhaps I will use uscf rather, or just both.
You should definitely use either FIDE or USCF if you want anything resembling a valuable conclusion. Otherwise, as they say, garbage in, garbage out. No conversion formula is 100% reliable (the way fide relates to uscf changes over time; uscf ratings used to be severely inflated in the past, but not anymore today; and this is continuously changing) and merging fide and uscf together pretending they are the same would be even worse. You just have to wait until you have enough data to use fide (or uscf) alone.