b.rb

require 'benchmark/ips'
require 'compel'
require 'dry-validation'
require 'dry/validation/schema/form'

params= {
  'first_name' => 'Joaquim',
  'birth_date' => '1989-0',
  'address' => {
    'line_one' => 'Lisboa',
    'line_two' => 'Madrit',
    'post_code' => '1100',
    'country' => 'PT'
  }
}

schema = Class.new(Dry::Validation::Schema::Form) do
  key(:first_name, &:filled?)
  key(:last_name, &:filled?)

  optional(:birth_date) { |v| v.date_time? }

  key(:address) do |address|
    address.hash? do
      address.key(:line_one, &:filled?)
      address.optional(:line_two, &:filled?)

      address.key(:post_code) { |v| v.filled? & v.format?(/^\d{4}-\d{3}$/) }
      address.key(:country_code) { |v| v.inclusion?(%w(PT GB)) }
    end
  end
end.new

Benchmark.ips do |x|
  x.report('compel') do
    Compel.run(params) do
      param :first_name, String, required: true
      param :last_name, String, required: true
      param :birth_date, DateTime

      param :address, Hash do
        param :line_one, String, required: true
        param :line_two, String
        param :post_code, String, required: true, format: /^\d{4}-\d{3}$/
        param :country_code, String, in: ['PT', 'GB']
      end
    end
  end

  x.report('dry-v') do
    schema.(params).messages
  end

  x.compare!
end

r.txt

Calculating -------------------------------------
              compel   311.000  i/100ms
               dry-v   355.000  i/100ms
-------------------------------------------------
              compel      3.222k (± 4.4%) i/s -     16.172k
               dry-v      3.591k (± 5.8%) i/s -     18.105k

Comparison:
               dry-v:     3590.8 i/s
              compel:     3222.4 i/s - 1.11x slower

Good call. I missed the fact you're using a symbolized keys-hash and Schema::Form is designed to work with stringified hashes. I updated the gist and indeed the difference in performance is minimal.