Data Filtering by Column/ Horizontal

SergeiBaklan 

First an observation.  Anything that can be done with LET could be done with named formula, I have used such calculations for years.  What you lose is the 'calculate once, use many times'; that would require helper ranges and not defined names.

The following gives both columns from a single spill but I wouldn't care to make any claims concerning computational efficiency!

= LET(
\1, "Filter range by date",
     firstRow, XLOOKUP(Start, NameTable[Date], NameTable, ,1),
     finalRow, XLOOKUP(End, NameTable[Date], NameTable, ,-1),
     filteredNames, firstRow:finalRow,
\2, "Calculate frequencies for filtered table",
    freqTable, COUNTIFS(filteredNames, filteredNames),
\3, "Unpivot both tables",
    m, ROWS(filteredNames),
    n, COLUMNS(filteredNames)-1,
    k, SEQUENCE(m*n),
    rowNum, 1+QUOTIENT(k-1,n),
    colNum, 1+MOD(k-1,n),
    nameList, INDEX(filteredNames, rowNum, 1+colNum),
    freqList, INDEX(freqTable, rowNum, 1+colNum),
\4, "Combine name and frequency lists",
    combined, IF({1,0}, nameList, freqList),
\5, "Sort unique on combined name and frequencies",
    SORT(UNIQUE(combined)) )

My indentation is not as interesting as yours because, in the main, I have used local names in place of nested formulas.  The jury is probably still out on whether one should write formulas like this; the fact that one can still has some shock value at the moment!