[RegexGenerator(@"[а-я-[аeиоуыэюя]]", RegexOptions.None, -1)]
private static partial Regex ConsonantRegex();

/// ...
/// I display only interesting part. 

/// <summary>Search <paramref name="inputSpan"/> starting from base.runtextpos for the next location a match could possibly start.</summary>
/// <param name="inputSpan">The text being scanned by the regular expression.</param>
/// <returns>true if a possible match was found; false if no more matches are possible.</returns>
private bool TryFindNextPossibleStartingPosition(ReadOnlySpan<char> inputSpan)
{
    int pos = base.runtextpos;
    char ch;
    
    // Empty matches aren't possible.
    if ((uint)pos < (uint)inputSpan.Length)
    {
        // The pattern begins with a character in the set [\u0430-\u044F-[e\u0430\u0438\u043E\u0443\u044B\u044D-\u044F]].
        // Find the next occurrence. If it can't be found, there's no match.
        ReadOnlySpan<char> span = inputSpan.Slice(pos);
        for (int i = 0; i < span.Length; i++)
        {
            if (((ch = span[i]) < 128 ? ("\0\0\0\0\0\0\0\0"[ch >> 4] & (1 << (ch & 0xF))) != 0 : RegexRunner.CharInClass((char)ch, "\0\u0002\0аѐ\0\u000e\0efабийопуфыьэѐ")))
            {
                base.runtextpos = pos + i;
                return true;
            }
        }
    }
}

public class DotnetRegexBenchmark
{
    // This is the pure copy from generated regex. 
    private readonly Regex _originalRegex = OriginalRegex.Instance;
    
    // This is the copy from generated regex with suggested change. 
    private readonly Regex _suggestedRegex = SuggestedRegex.Instance;
    
    // Text with Latin symbols.
    private readonly string? _text;

    public DotnetRegexBenchmark()
    {
        _text = new string(Enumerable
            .Range(1, 5000)
            .Select(i => (char)('a' + i % ('z' - 'a')))
            .ToArray());
    }

    [Benchmark(Baseline = true)]
    public int Original() => CountMatches(_originalRegex);

    [Benchmark]
    public int Suggested() => CountMatches(_suggestedRegex);
    
    private int CountMatches(Regex regex)
    {
        int matchesCount = 0;
        Match match = regex.Match(_text!);
        while (match.Success)
        {
            ++matchesCount;
            match = match.NextMatch();
        }
        return matchesCount;
    }
}