The more I think about this, the more I think that the suggestion that a verb such as μακαρίζω would be needed to makes this sense clear. I don't have the time to check examples now, but I just don't think μακάριος can be used in this way, as though it is a substitute for a passive verb. The adjective is not truly a passive idea, though we used a passive form "blessed" as one of the English renderings. Also, throughout the passage, μαρκάριος is a predicate adjective with the implied verb εἶναι. This is followed by the reason for the blessing. Your rendering messes with the structure and especially the parallelism of the statements, "the poor are blessed by the Spirit because theirs is the kingdom of heaven" just doesn't follow what each of the other couplets are saying. I don't think Eph 1:13 is truly parallel because the dative is placed to limit the expressed verb, whereas in Matt 1:3 it is placed in a very convenient spot to limit πτωχοί. Note also BDAG on πτωχός:Thomas Dolhanty wrote: The instrumental (means) dative should not be a surprise here. There is no need in Koine to use ὑπό in such a context. The dative will do the job just fine. For example:
… ἐν ᾧ καὶ πιστεύσαντες ἐσφραγίσθητε τῷ πνεύματι τῆς ἐπαγγελίας τῷ ἁγίῳ, Eph.1:13
I would make τῷ πνεύματι here a dative of means. Note also the passive voice and the unexpected (to me at least) placement of τῷ ἁγίῳ.
③ lacking in spiritual worth, fig. ext. of 1 (Tat. 6, 2 of humans ὁ μὲν πτωχός [in contrast to God]) οἱ πτωχοὶ τῷ πνεύματι Mt 5:3 (cp. 1QM 14:7 עַנְוֵי רוּחַ; s. πνεῦμα 3b and Goodsp., Probs. 16f;; EBest, NTS 7, ’60/61, 255–58; SLégasse, NTS 8, ’61/62, 336–45 (Qumran); HBraun, Qumran u. d. NT I, ’66, 13; LKeck, The Poor among the Saints in Jewish Christianity and Qumran, ZNW 57, ’66, 54–78; add. lit. Betz, SM 111). The ‘messenger’ of the church at Laodicea, who says of himself πλούσιός εἰμι καὶ πεπλούτηκα, is termed πτωχός Rv 3:17. In 1 Cl 15:6, Ps 11:6 is quoted w. ref. to the situation in the Corinthian church.
Arndt, W., Danker, F. W., & Bauer, W. (2000). A Greek-English lexicon of the New Testament and other early Christian literature (3rd ed., p. 896). Chicago: University of Chicago Press.
Also, see vs. 8:
8 μακάριοι οἱ καθαροὶ τῇ καρδίᾳ,
ὅτι αὐτοὶ τὸν θεὸν ὄψονται.
I don't think anyone would read this as "the pure are blessed by the heart..."