Dont want to do big investment but want to have share back?
tell you guys one thing, many years ago CMHK (China Mobile Hong Kong) was a MVNO and it does not have 3G spectrum at all, it is a big company in China but not in Hong Kong.
CMHK was riding on someone else 3G network but its quality cannot be controlled, poor coverage / very slow speed on 3G network.
After a few years, HK gov had auctions for spectrum re-allocation and CMHK invested a lot on the 3G / 4G spectrum, also invest a lot on cell sites as well.
Now CMHK has its own network, not a MVNO anymore and offering affordable plan to people, especially CMHK mother company has advantage in China and it offers affordable China / Macau roaming plan as well... (like 1C2N service, call receiving is free in China / Macau, affordable price of 5G data roaming in China / Worldwide, etc..)
for such behavior DNB do all 5G cell site coverage, not only taking about technical side it would be difficult to handover as well, it would be a "single point of failure" as well. also discourage investment or innovation on 5G technology (for example, VoNR, 5G CA... etc...) because less of competition.
the 10 years contract with DNB is also less flexibility to carrier, 10 years later we may be talking 6G already and 5G may become very basic or cheap technology probably in other country, while our carriers are still bounding to that contract and paying expensive rental to DNB....
and I found a big issue today, Yes 4G is not able to distinguish the traffic is from 4G or 5G, when I do the speedtest from my phone using 5G network, LTE data consume first and I received sms that LTE prepaid data is finished while the plan I have also contains unlimited 5G data.
it seems that not only about how to allocate (or sell? ) the DNB share to different carriers , on technical aspect it was unable to handle smooth handover from 5G to 4G, not able to distinguish 4G/5G data and deduct wrong data from my plan (fortunately it is free 5G trial and all data are redeemed from Shopee).
My personal recommendation is until all of those issues are fixed, otherwise it is not worth to pay extra $$ to have 5G plan now.

your concerns also shared with these large telcos. they worry about quality of service QOS should they go with DNB/1MDB 5g. they worry about customer complains about exactly what you having. That's why telcos cannot agree with DNB/1MDB 5g about the pricing and such until today.
telcos wanted to build their alternative infra to DNB/1MDB 5g but were turned down by gov. what else they can do anyway? DNB/1MDB 5g from start is a mistake as its only real objective is just to enrich the cronies. besides that also make the 5g investment of major telcos within these 3 years become null and void