The more the better for security, the upper practical limit is golds inflation rate, the lower practical limit is the percentage of coins that become lost or inaccessible. That puts the viable range to 1.5-0.2%, roughly. To be clear, I'm not worried about bitcoins current rate, but rather that it will drop further and further.
itsmect
You are clearly knowledgeable about the things you're talking and made a conscious decision. It seems like we agree that there is some risk, but you consider it insignificant while I it's quite substantial. Only time will tell whose right.
Monero's inflation is not a percentage, but rather a fixed 0.6XMR per block. This mean as the supply grows, the inflation percentage will slowly go down, so there's no exponential losses like with fiat inflation. Currently the 0.6XMR/block work out to 0.9% of the mcap, in the year 2100 it will be down to 0.5%: https://moneroj.net/tail_emission/ (<- great site btw, it has a few BTC diagrams as well). The tail emission was chosen so that it works out to be less inflation then gold, but high enough to have a decent security budget.
Bitcoins current budget is sufficient at about 1.6% (= 8B USD) annually. After next halfing it will be about 0.8%, similar to Monero's budget. In 2032 it will be about 0.2%. If Bitcoins price doesn't increase, the budget would only be 1B USD; if it does increase, a 4T mcap would be secured by still only secured by 8B. Either way, the more time passes, the easier Bitcoin becomes to attack. How much longer do you think bitcoin will last?
The (original) selling point of crypto is that it can't be manipulated, even by nations with practically unlimited power and funds. Side chains sacrifice some of the immutability for other aspects and are a at best workaround instead of solution. So far there is little evidence to show that transaction fees will one day make up for the loss in block rewards.
The primary competitor to Monero is not Bitcoin, but gold, whose inflation sits at about 1.5%. Proponents of tail emission have long left bitcoin, and rather contribute to a project which aligns with their views. The remaining crowd will therefore be biased, don't take their word as gospel.
The security budget is total fiat denominated miner reward of the entire network. The higher it is, the the more resistant bitcoin becomes to 51% attacks.
As you know, each halfing decreases the block reward, which is currently the largest part of the total miner reward. In order keep a steady security budget, the price and market cap has to double each time as well. But remember, the security budget stays constant, so an ever increasing amount is secured by a relatively lower share.
Transaction fees make up the remaining tiny share, and I honestly don't see it growing much. Because the higher this fee becomes, the more people will find ways to avoid it, and just keep it on exchanges, custodial solution or lightning. This reduces the decentralization , the primary feature of bitcoin, and thereby reduces it value proposition.
All this can be side-stepped by having holders pay a small, program-ably guaranteed fee proportional to their holdings, which is then paid out to miners. Yes, this is similar to inflation, but as long as it is lower than fiat inflation I can be worth the trade off. Considering how cult like bitcoin holder are, I don't think this is a change they are willing to make, at least not before it's too late.
I didn't talk about features, but specifically about the security budget.
Tell me again which one is the best place to store value?
I don't think you are ready to hear this yet, but it's monero :P All jokes aside, bitcoin ain't terrible, especially compared to the dollar, but I worry that botcoin's security model will crumble more with each halfing. Transaction fees are already unusable in some cases, yet they barely contribute to the miner rewards. The math doesn't seem to work out.
The goal is to create attractive market conditions. Positioning yourself between the historic store of value and the minimum to avoid deflation seems like a good target.