Yes, but now there are counter measures in place, namely: Segwit, and LN. Dec 2017 was quite exceptional, if things remained the same (no segwit, as a group wanted) you could probably predict the exact same thing occurring again. But now, even if tx fees rise up a little, i don't think it will be as dramatic as those 3 months.
I agree and the implemention of LN will also be very interesting to see how tx fees are affected. Currently, the trend could be that the percentage of transaction fees per block will go down short-term and just be extended to keep slower increasing for future halvings.
But finally in LN there will always be on-chain transactions (tx fees go to miners) and as conclusion the following results can be possible:
- much higher number of transactions are done off-chain (multiple off-chain transactions are funding the final on-chain transaction)
- long-term on chain-transactions could be more expensive
- single transactions on LN will be much cheaper
But that could be another thread about LN affecting tx-fees. Of course, that's not a final solution.
In addition, small tx fees will be another advantage for BTC and make a higher price for BTC more likely. The argument that BTC transactions are too expensive would be flawed.
Mining profits are destined to go down regardless. Coin price has delayed this somewhat, but in the long run is a lost battle. The last miners will be those with free electricity, such as those that invested in solar back when they could have spent it all in more Asic miners. I cannot stress this enough: Buying only asics and no renewables means you won't stay for long. Incidentally too large operations will go as well, smaler more efficient farms using renewable energy will outlast the giants using the grid. Some people without discipline expand beyond their capacity because they don't think long term. Even with higher bitcoin prices, mining will become more and more unprofitable, as designed.
For now I don't see a problem for most miners to get unprofitable. The difficulty is still 3 times higher than December 2017 when BTC had the last ATH. There is still a lot of time left until the block rewards will decrease to a significant low level. If we assume that the BTC price will be much higher, the price will also be higher per block reward. Of course that's not waterproof for now.
We should remember that we are currently at a very low level of tx fees:
https://btc.com/stats/feeLong-term your assumptions are indeed justified but there is still time to improve things and I'm sure there will be good solutions.