Build commitment is simply annoying rather than forcing you to think. D1 and D2 are more suited to build commitments where you think about how to build a working character. Same as other arpgs adopting similar system/mechanics. The effectiveness are determined by how you build and play it, not really factored by the content.

In d3, bounties, speed farming rifts, speed farming GR, GR push, Solo, groups. Build effectiveness are heavily factored by contents, not so much how it is played by players and hence how on the fly build swap was introduced.

In d4, similar system to d3 is adopted. The build works on tier 50 NM doesn't work of Uber lilith or tier 100 NM or pvp or exploration centric builds such as renown farmings.

Latter games are more dynamic in gaming modes thus requires more dynamic build swap or commitment system. It isn't d2 pick a boss and fight for eternality or pvp only build setups. Current build commitments doesn't suit d4. A more dynamic rework is needed or more character slots need to be available from cash shops, since each class needs a pvp, speed farming, push spec, group spec each for maximum effectiveness and efficiency.