Getting all descendants IWebElements (using XPath) is too slow in Selenium

Question

Well, I'm working with Selenium to scrape a webpage that has obfuscated class names (example <div class="example-gHJkLM">...)...

So I needed to create an extension method to get

public static ReadOnlyCollection<IWebElement> Descendants(this IWebElement element, bool hasChildren = false, int index = -1, string postAppend = "")
{
    var web = element.GetWebDriver(); // < 1ms
    var xpath = element.XPath(); // 5 ms

    return web.FindElements(By.XPath(xpath + "//" + (hasChildren ? "child::node()" : "*") + (index > -1 ? $"[{index + 1}]" : string.Empty) + postAppend)); // 64 ms
}

public static ReadOnlyCollection<IWebElement> GetNodesByContainingClass(this IWebElement element, string className,
    bool toLower = false, bool useFullHierarchy = false)
{
    return new ReadOnlyCollection<IWebElement>(element?.Descendants()
        .Where(n =>
            (toLower ? n.GetAttribute("class")?.ToLowerInvariant() : n.GetAttribute("class"))
            ?.Contains(className) == true).ToList()); // ????
}

public static IWebElement GetNodeByContainingClass(this IWebElement node, string className)
{
    return node?.GetNodesByContainingClass(className).FirstOrDefault();
}

Example usage:

            var watch = Stopwatch.StartNew();

            var welcomeMessage = messageBox
                .GetNodesByContainingClass(
                    "icon-", false, true)?
                .LastOrDefault();

            watch.Stop();
            Console.WriteLine($@"[Getting welcome message element] Ellapsed {watch.ElapsedMilliseconds} ms!", Color.Yellow);

• messageBox is a IWebElement
• I'm using Colorful.Console package

And this is what I got:

4 and 9 seconds to materialize a Where LINQ clause, seriously? I debugged the element?.Descendants() part and this has only 727 elements...

Can anyone guide me?

Also, I will be so thankfully if somebody suggests me a better approach to do this.