Bitcoin's layer 1 is operating at capacity - different networks make different tradeoffs. Bitcoin has gone the "less change" and "more decentralization" route by keeping layer 1 small, with the goal of moving transaction volume to layer 2.
Bitcoin introduced a number of changes like SegWit that are way more complex than adjusting a constant on layer 1, plus a huge amount of complexity on layer 2 that makes using layer 2 just as complicated as (or more complicated than) using a different cryptocurrency.
Whether it leads to "more decentralization" when everyone can run their own (L1) node but a single L1 transaction costs as much as the node hardware is quite debatable IMO. By making L1 transactions unaffordable, it encourages _centralized_ solutions where IOUs are shuffled around entirely off-chain.
Even if second layer solutions become highly centralized, the risk is significantly mitigated if you just don't keep your savings on them. If popular second layer solutions become untrustworthy then it would be easy to switch to different ones.
- Bitcoin is operating at capacity and has shown unwillingness to adjust capacity, so the "kWh/tx" is valid for Bitcoin.
- Transaction fees increase the block reward, and as a consequence, the energy that can be used for mining before it becomes unprofitable. This is currently only about 10% of the total reward miners get for mining a block on the Bitcoin (BTC) blockchain, but it is something to consider. The corresponding part of the energy usage would, at a fixed fee, be proportional to transactions.