Would it really take 5 years to develop rare compress and decompression that seems an extreme overestimate in time. I don't know of the compressor decompression but that seems really high
Well, it is every version of RAR. Documenting the quirks of rar 1.4, 1.5, 2.0, 2.9, 3.0, 4.0, 5.0 and 7.0, multiple compression strategies, PPMd, RARVM, compression levels, encryption, multi volume support, a huge test corpus, round trips for compatibility... The spec docs are linked.
Your probably right I should read the spec but I've worked with so many brillant engineers and I am still pretty young so their must be even more. I just think the overselling of complexity is usually what makes things enterprise grade :) (if you know you know)
5 week is a decompressor for 1 version. If this supports multiple versions of RAR, then writing decompressors alone for all of them is probably a year effort of work.