Up to 4 monsters that have 100 ATK or 100 DEF, there's not many good monsters to summon and even if it opens up synchro plays (which it does), you wouldn't be able to use his eff and when he leaves the field all monsters in the graveyard (which is the clause I missed, really sorry about that :[ ) all of the monsters with 100 ATK or 100 DEF get banished, so it means you'd have to sync with him last in the combo.
Honestly, I think the effect that is actually broken is the synchro summon, not the summon 4.
They're all broken in different ways and means.
Honestly not even sure how to explain to you that the first effect is totally unjustifiable because it really should be self-evident.
The second effect is actually in some aspects kinda bad, but it's possibly even worse designed because it's only useful if you can do a full resolution of the first effect, so it's only useful when hinging off a broken effect. The effect itself doesn't really seem inherently broken, but giving 4k no-response is also difficult to balance with different requirements, so it's probably just the context of requiring a Tribute 4.
And the 3rd effect is also broken, yes, with being able to be sent from anywhere and pump out Synchros on the cheap (for the record, if this card is the only 1 sent, it's the only one that gets banished--meaning you can just Foolish a Naturia Beast).
No OPTs on anything certainly doesn't help the issue. At least it's hard to resolve the first effect multiple times when the last effect banishes all targets?
Also, for the record, your PSCT was pretty bad but that is usually the last category I consider when rating a card, despite what frenzyhero may prefer.