Idle thought... Would the Celestials generate so much discussion if they were still the dedicated rides of the MD, but less... quirky? They have a buzz about them for being durable because with the exception of the Archangel, they all use LFEs and they are all 94% of max armor or better. So are a lot of other mechs in 3075. Yeah, they all uses small cockpits, which makes them a good deal for MD pilots, but there are other mechs out there that do the same. Light mechs and artillery/fire support machines can make good use of that extra ton. Lights generally don't survive many turns of taking 20+ damage at a clip and I think +1 PSR in exchange for an extra bin of Arrow IV is a good trade.
As a whole, the Celestials are well armored, they don't suffer from side torso kills, and assuming a pilot with VDNI, they don't suffer for having a small cockpit. On the other hand, they don't suffer too much in the way of pod space either. The IS Omni population is fairly small but a couple spot checks comparing the Celestials to the other IS Omnis in 3058, 3067, and 3085 doesn't show them to be overly lacking in available weight. I didn't get into comparing free crits.
Yeah, they use a lot of light and heavy PPCs, so do a lot of machines 3075+. Interestingly enough, none of the Celestials VSPs until SB:Wolf and Blake, but Tengu heavy BA, and Rusalka heavy Omnifighter do.