The thing about comparing with Lenovo acquiring Motorola was that just like Motorola changed the game of budget Android phones back when original Moto G released, OnePlus changed the perception too with their initial line-up of Android phones, catering to audience who wouldn't go for brands like Samsung, Sony or LG.
And lack of good Pixel devices in India, added to success of OnePlus as a brand that attracts enthusiasts. Same can't be said for Oppo which just tries to upsell mediocre phones in the offline market, just visit any mobile phone store locally which has one of those huge Oppo Banners and you'd know how the shop owners will try to sell you an overprice Oppo phone stating that it is better than Xiaomi counterpart. And OnePlus attracted a lot of bad rep with Android 11 redesign that they launched late last year which looked exactly same as Samsung One UI.
TL;DR
OnePlus was a brand recognized and loved by Android enthusiasts, and their product direction is now going mainstream (which makes sense from business perspective) and that wouldn't help them retaining loyal users.
To add to it, I highly doubt that OnePlus would allow unlocking bootloaders or even release Kernel sources on time in the future.