consensus of more than 50% total network computing power
Computing power has nothing to do with hardforks.
Hardforks are not a great path to evolution. They're dangerous and potentially coercive. They must be undertaken with the consent of effectively _all_ users. They should be avoided unless there are no other reasonable alternatives.
Although many things have changed and advanced, it's arguable if we've ever had a hardfork or not: Very old nodes can still validate the chain, though they will non-deterministically fail because of semi-hard-forking database management bugs that have been fixed.
Fortunately, we don't have to have hardforks to evolve: The P2P protocol is a matter between individual peers. They can negotiate whatever options they want. We have replaced the p2p protocol. Most interesting and important changes to the blockchain validation rules can be accomplished via softforking changes. E.g. P2SH is effectively a radical change in how transaction spending rules are encoded and was accomplished without a hard fork.
In Bitcoin evolution is slow. There are wallets which cannot be updated because they run on platforms controlled by corporations which are hostile to user-freedom (in particular, there is an i phone wallet app that produces signatures with an invalid encoding). There are multiple implementations of the Bitcoin protocol, but even with the BIP process their implementers have simply declined to implement some functionality, and its lack of universal availability makes it unusable to users. etc. But the system itself is a gigantic moving machine and failure is difficulty— even impossible— to fix, if something goes wrong so it's hard to say that slowness is a bad thing at all. Slowness helps ensures there is understanding and consent and reduces risk.
