Lacking audibility? People can just give view keys to audit.
If youre are talking about xmr creation that's calculable. Range-proofs allow it to be mathematically proven that the inputs and outputs of each transaction add up to zero without revealing amounts, ensuring that the supply is sound and not inflated in any way.
Every node runner can verify max supply themselves as well, though this is harder and more time consuming than Bitcoin.
Monero prevented ASICS to ensure it wouldn't be as susceptible to 51% attacks.
You are correct Bitcoins blockchains is smaller but Moneros bloat has shrunk throughout its history and will likely continue to do so. This is the cost of everything else being so useful.
A decent post on this is here:
https://sethforprivacy.com/posts/dispelling-monero-fud/#you-cant-audit-the-monero-supplyThe biggest disadvantage Monero has against Bitcoin is an economic one: the tail emission. It's harder to market a technically infinite but disinflationary (ie, always approaching 0% inflation but never reaching it) currency compared to Bitcoins max supply.