Xabi Alonso is not yet comparable to Pep Guardiola, but maybe he will be after he has a lot of flying time and a collection of titles. Pep Guardiola is one of the most successful coaches of this decade, while Xabi Alonso has just started his professional career as a coach. Xabi certainly has good abilities as a potential big coach in the next few seasons, but comparing him with Pep Guardiola at the moment is not appropriate.
Xabi Alonso is just fortunate to make a mark in Europe and the Bundesliga within a short period. He became the first coach in the German League to go unbeaten all through the season and the longest unbeaten run in Europe (51 games). Pep Guardiola might not have such remarkable career numbers, but he is one of the greatest coaches of all time. Pep has gotten more experience and won more trophies and awards than the young Spanish coach.
I agree that there will be many new coaches who will emerge as top coaches for European teams. Xabi Alonson, Arteta, Xavi and several other Spanish coaches have the quality of providing competition, but all of them do not have the same path. Whether a coach is successful or not depends on the depth of the squad, financial support and several other technical things, so definitely not all of them will be successful.
The success of the coach depends on the players, management support, and availability of funds. But let me add that luck can play a significant role. Bayern Munich had the best players, coach, and money, but it looks like Mother Luck favored Bayer Leverkusen. We have seen many young coaches leading top clubs; all eyes will be on Russell Martin, Kieran McKenna, Fabian Hürzeler, and Vincent Kompany.