Alonso, speaking with Leverkusen on the brink of the Europa League final, congratulated Dortmund for making the Champions League final after beating Paris Saint-Germain 2-0 on aggregate on Tuesday.
Bayern Munich can make it an all-German final by defeating Real Madrid in their finely-balanced second leg on Wednesday.
Then Leverkusen can book their place in the Europa League showdown on Thursday if they can hold onto their 2-0 lead from the first leg against Roma.
Alonso’s side were crowned German champions for the first time in their history in mid-April and are on a season-long unbeaten run of 48 games in all competitions this season.
“This high level in the Bundesliga means what we’ve been able to do is not easy,” Alonso told reporters.
“It’s very positive for the Bundesliga. I should congratulate Dortmund and congratulate Edin (Terzic, their coach), it’s not easy to make it to the Champions League final.
“Yesterday they played as a team so congrats to them.”
Leverkusen can break the record
Leverkusen can break the record for successive unbeaten games set by Benfica in 1965 by avoiding defeat against Roma and are two league matches away from being the first side to go through a Bundesliga season unbeaten.
Alonso played in the Bundesliga for Bayern as well as with Liverpool in the Premier League and for Real Madrid in La Liga before becoming a manager.
He was linked with Jurgen Klopp’s soon-to-be-vacant manager’s job at Liverpool and the hot seat at Bayern Munich but has said he will remain at Leverkusen next season.
Alonso was asked whether the English league’s claims of being the best were warranted with no teams in the final four of either the Champions League or Europa League this season.
“You can say anything you like, but results are results. They’re facts you cannot discard them,” the Spaniard said.
Leverkusen only need to avoid defeat by more than a goal at home against Roma on Thursday to progress to the final in Dublin on May 22.
The 42-year-old manager said “A return leg is always a dangerous situation. No matter what the first result was, a goal can quickly change the situation and the mindset.
“We want to be aggressive, to control the game, and to defend well.”
Last season, Roma defeated Leverkusen over two legs to make it to the final and Alonso said the bitter memory of that May evening would motivate them.
“We haven’t forgotten what we experienced in our stadium and the feeling we felt last year.
“We must use this energy and hopefully we can celebrate at the end.”
Leverkusen defender Edmund Tapsoba echoed Alonso’s statements, telling reporters “we saw last season how our fans suffered after the defeat against Roma.
“We want to give back to them for what they did for us this season.