Indonesia has been quite passive a leader in ASEAN to be honest. Indonesia needs to be much more assertive and needs to show its leadership in a more open role than taking passive stances in most crucial issues. That's how a leader should behave, just being the biggest doesn't means you are automatically the leader, you have to earn and show it.
However, i don't think Australia will allow Indonesia to be more assertive in this role, since it wont be to Australia's interests either. So therein comes the dilemma as well.
I dont think what you said is true, actually many importance initiatives have been made by Indonesia within ASEAN that in the end were followed by other members. Indonesia Indo Pasific concept adoption by the group become the latest of such leadership showchase. Indonesia also in the past blocked Mahathir initiative to make East Asia Forum that will kick out US from the region. Indonesia always want US to be included and it is what becomes the reality and now it is clear who has better vision and comprehension about potential threat after China becomes more aggressive in SCS under Xi leadership.
It is always Indonesia traditional point of view since Soeharto regime to see China as a threat where one of the main reasons of it is always about its traditional nine dash line claim that China still hold although during Soeharto period China doesnt acted as aggressive as in recent decades, but recent event after China economic rise has proven that the worry is justified. It shows Indonesia foreign strategy is more mature and clever despite a bit more conservative and much less innovative and aggressive that give an impression that Indonesia diplomacy is rather passive than active.
Indo Pacific concept that is adopted by ASEAN in the middle of June 2019 has a very importance point which say about the obligation for all parties in the region to follow international law to resolve territorial dispute between them. This is a very important point that shows ASEAN is still solid and has become more blunt to oppose China nine dash line claim that has no international law (UNCLOS) basis, and it is later strengthen by a historic event in late January where all ASEAN foreign ministers made a commitment which says that ASEAN as a group rejects any territorial claim that doesnt inline with international law (UNCLOS).
The event also shows China economic influence and diplomatic work in countries such as Thailand, Myanmar, Laos, and Cambodia cannot divide ASEAN into two camps, and what has become Indonesia vision about ASEAN turns into reality which is against China diplomatic goal to divide ASEAN and make the group become impotent when it comes to SCS matter.
Indonesia itself has become more aggressive on his stance about China nine dash claim recently by using Philippine winning case as an example, not long after the joint ASEAN committee in late January. This diplomatic move has made Indonesia as the first country in ASEAN to use Philippine winning case to oppose China nine dash claim. So it look like Indonesia recent stronger stance is likely to be already strategically planned where the first step to take is to get ASEAN backing through its Indo Pacific doctrine that is adopted by ASEAN in June/July 2019. The process to reach that diplomatic goal of course is smoothend by the fact that Vietnam, Philippine, Malaysia, and Brunei are also against China nine dash line claim.
This shows Indonesia active role and its influence in the most important peace process in the region.
Example of Indonesia influence and active diplomacy in ASEAN during Soeharto regime
1. Peace Process in Kambodia
https://en.wikipedia.org/wiki/1991_Paris_Peace_Agreements where the signatory is France as former colonials and Indonesia (only ASEAN members)
2. 1996 Final Peace Agreement between Bangsa Moro and Philippine
The peace process is also called as Jakarta accord to show huge Indonesia contribution to the peace process. The signatory is Philippine government, Moro National Liberation Front (MNLF), Indonesia representative (the only ASEAN member), and Nigeria representative
en.wikipedia.org
After reformation/Indonesia turns into democracy (1998-present)
3. Thailand-Cambodia border conflict become military classes in 2011 and two parties agree to let Indonesia as the only observer to be deployed to the disputed region which shows once again that Indonesia active participation to mediate the conflict and its weight among ASEAN members
On May 7, 2011, Thailand and Cambodia agreed to appoint Indonesia as observers at the disputed border.
[134][135]
en.wikipedia.org
